Dave, the big question would be....what kind of tone are you looking for? That's where the answer really lies. If you want a classic rock tone, you're better off shopping for gear that excels in that. The problem there is...sometimes making classic rock tones come to life can take a little time and mic patience.
If you want versatility, amp modelers do a fair job, but in my experience they seem to fall short live yet, they rock for recording. I don't even know if they still make these, but I played a show in the UK in 1999. My first time touring over there. I had thought I had all my bases covered with power converters etc, but I was way off the mark and my rig never fired up.
There was another band playing before me and the guitarist let me use his head. It was a Line 6 Flex...the first version they ever made. I was completely impressed by this head. It had a wide array of options, onboard effects, its own pedal board with expression pedals and it didn't even bother me that it was a transistor amp. I like to at least have a 12AX7 front end and don't really care about output power tubes....I don't need to be that loud to where they would come into play. But that amp was pretty killer.
I went to a music store a few years later and saw they had a Flex II version of the amp. This was even more killer than the one I tried. I nearly bought the thing "just to have" because it sounded great and could deliver just about any sound. They also upped the gain stage in it compared to the one I tried. So definitely look into that if they still have those available.
Another thing you may want to consider...I had a guy come into my studio a few weeks back that brought this little Peavey combo amp with him called a Vyper. They come in two versions...tube and tranny. He had the tube amp. Man, I was simply blown away at how great that little amp sounded. Again, onboard effects and a nice pedalboard is available. Definitely check that amp out even moreso than the Line 6. I plan on buying one the next time I call in a Sweetwater order. It must be nice to live near them...haha...I love that place. But seriously, check that amp out. It comes in a combo and a head version. You get from modern metal to jazz fusion and chicken pickin' sounds in an instant with all the warmth, sustain and "feel" of tubes.
If you're not interested in buying a new amp and are maybe searching for effects to drive what you have....sometimes this is a tough situation to be in. Tone sculpting is a lot like "fixing a tone in the mix". What I mean by that is, many times during our lives, we record sounds that simply don't work and we spend countless hours trying to fix these tones in our mixes. The same can be said for working with gear that just may not be capable of giving you the sound you are looking for and if you're not careful, you could spend a lot of money trying to make this stuff sound good and fail.
The marriage of certain amps and certain cabs is of the utmost importantance in my opinion as well as having an amp that really has a good sound coming out of the gate. Just like recording....garbage in, garbage out. Once you're at the garbage stage, most times you're not going to improve the sound no matter what you do. You definitely need to get the right tools for the job.
For example, a cleaner driven rig like MakeShift Mike's (he has a really good light gain rock tone by the way) is not going to get you the sound of John Petrucci or the Nickelback type tone. Most of that high gain stuff (if that's what you're into) is going to come from a tube amp with a really good pre-amp section. Like for example, quite a lot of my friends hate Mesa Dual Rectum Fryers. I think they are one of the sickest amps right out of the box for rock or metal. Me personally, I'm not an amp user anymore because I found my pleasure and versatility out of using my 2101 tube pre-amp into a power amp and then into my cabs. And, my amp rack was nearly as heavy as my effects rack. LOL!
But the first thing to look into is what type of sound you want. From there, once you can create the front end to where it sounds great, then you can look into effects to enhance it if need be. But it starts with the front end sound. For example, if you plug into your amp straight right now and right into your cab, do you like the sound? If the answer is no, it's probably not going to improve much unless you get a new head or change your cab. It's amazing how different an amp can sound once you find the right cab partner for it. I've been through so many cabs and speakers bro....it would make your head spin.
But you have to find out where the source of the problem is. For me, I knew my front end was always good, but I always found myself messing with my eq's constantly. The cabs I was using were just not complimenting my tone. So I brought my amp with me to the music store one day and went through every single cab they had. I was never a Marshall/Celestion fan because to me, those speakers just sounded bad no matter what. However, I had never heard of Greenback 25's....and as soon as I plugged into that cab, I came home with 4 of them and have been using them ever since.
The good thing about them is, they are very warm compared to the other Celestions. And, because the wattage is so low at 25 watts per speaker, the break-up is awesome to where you can literally use less pre-amp gain and allow the speakers to do their job. The only 2 downsides are, it's pretty easy to blow a cab if you are into extreme volume. I'm not a loud guitarist, so I've never even blown them up in all the years I've owned them thank God. (touches wood)
The second thing is, they are a VERY focused cab...meaning, they were made for mic'ing at close range and sound fantastic for recording and live through a P.A. After about 8 feet or so, they sort of lose their sound....but no one should ever be that loud to where your stage volume it blowing peoples heads off to where they hear that anyway. I'm so low on stage, it allows the soundman to do his job and he puts me through the monitors, so I can always hear myself.
So you may want to do a little soul-searching with your cab or maybe change your head....or maybe even consider a pre-amp. The 3 best tube pre-amps that I have here are my 2101, a Mesa Tri-Axis and an old ADA Mp2. The Mesa stays in the studio because it's very versatile and also can't change programs fast enough for live performances. I have this pet peeve when processors have a glitch/delay in the preset change. It makes me nuts! The other thing you may want to consider that would probably be the be all end all of processors is the AxFxII.
It's incredibly pricey at nearly 3k with a waiting list, but they broke the mold when they created that pre-amp. There is nothing it can't do. You can even take a sound off an album where the sound is playing by itself, and it will cop the tone in seconds. I had a guy record with one here and he left it here for the duration of his sessions. Man did I play with that thing! LOL! I'm definitely considering getting one because of all the options it has that nothing else does...and it sounds great. My only issue with it is, it would have been complete if they gave it 12AX7 tubes. I just like the sound of a tube pre section as well as the over-tones and pinch harmonics it gives me. Transistor amps sort of get this weird, fake sound when doing pinch harms that are WAY different when you use a tube rig. That's not a deal breaker for me of course, but it's something that is important to me.
So give this stuff some thought. You may just be better off starting fresh with gear that will give you the sound you are looking for right out of the box instead of trying to create something out of gear that may never get what you're looking for. Good luck man....keep us posted.
-Danny