Has been a fantastic SudioCat computer.  Got some time on it now and wondering what something shiny and brand new might do.  No real complaints for sure right now, so not really sure an upgrade is really worthwhile.  Sonar projects with lots of plugs and VSTi play just fine at my lowest latency.  I have to have 20 VSTi or more before something wacky might happen.  I guess that's the RAM?
Just looking to stay current.

I've just done a whole upgrade of my Toshiba 16 gig ram, 2 gig AMD graphics card and an i7 CPU...I think similar to yours - I brought this at the start 2015.
 
I was having some difficulty after the last Windows upgrade with the graphics card, and after I decided to use Sonar's full 64bitfp architecture. Basically I could not do a large mix and master at the same time - 30-50 tracks multiple Wave's and Cake plugs. Whilst the CPU on my Toshiba was fine, the memory and the graphics memory were struggling. So to answer your question, a new CPU if your computer is running fine won't really do much. You'd be better off with a Thunderbolt port, and a new Thunderbolt audio interface...this theoretically would give you the ability to play VST effects like Guitar Rig and have latency that was not discernible. 
 
Where you might find a new CPU useful is if you were doing video editing and rendering, something I do also. My old laptop would take 4 hours to render 5-10 mins of footage. Admittedly, I was using the 2 pass option in Vegas Video, and a variable bit rate of 50,000. The render time of my new laptop is between 40-60 mins. 
 
CPU is no longer, I believe the benchmark to measure an audio computer by. Sure, the best CPU will cut down render times for video processing. And indeed, even though my new laptop is an i7 8th gen, apparently the 9th gen CPU would cut down video rendering times even further.
 
For what it is worth, and this will be very unpopular for those wedded to unwieldy desktops - but a good, not even top of the line P.C gaming laptop these days will suffice for all audio work. This is 64bitfp 96khz - although I would not be able to tell you how many tracks you will get to play. At 64bitfp 48khz - i'm finishing a piece at this sample rate - I'm running 58 tracks, and master buss effects...but this is the upper limit of the machine. I freeze all my individual tracks, so that frees up a lot of resources. I have about 10 aux tracks, and 5 busses running though, with each of these tracks containing a number of CPU/Memory hog Wave's plugs like the J37 tape emulator, Wave's NLS on each track, and a slew of tasty EQ and compression tracks.  
 
The specs of my Acer Nitro laptop are 32 gig of ram, 6 gig of graphics ram, internal SSD drive, and a second spindle drive for storage - I have an SSD drive connected to a USB 3 port for audio. The laptop has a Thunderbolt 3 port, so when I can I will be able to connect an audio interface to this which means the machine is future proof (up to 3 years). Not enough?? How about 4k ips monitor, and I've hooked up a second 4k monitor and both are running at 60hz or 60fps refresh rate. It's a sweet ride :) and all for the glorious price of $2500 Oz, so even affordable for those who would prefer a 'pro' audio rig.   
 
Hopefully this answers your question.
 
Ben      

Your existing system isn't terribly old/slow.
Depends on what you want to accomplish...
 
A comparable current machine would have the 7700k (quad-core at 4.5GHz - 8 processing threads).
The 8700k will be available in quantity around the Holidays (hex-core at 4.7GHz - 12 processing threads).
Compatible motherboards now max out at 64GB RAM.
The 7700k and 8700k both provide 40 PCIe lanes.
 
If you're wanting more processing power... but don't want to stretch to an i9 based system, the 6850k is a great balance of cost/performance (hex-core at 4GHz - 12 processing threads, quad-channel RAM up to 128GB).
The 6850k provides 40 PCIe lanes.
 
If you want to go high-end, the i9 7900x is amazing (10-cores at 4.5GHz - 20 processing threads).
For those working with video, the i9 series really cut down on render times.
ie: If you've got deep pockets, the 7980xe has 18-cores at 4.4GHz (36 processing threads).
The cost seems outrageous, but it can save hundreds if not thousands of hours of rendering time per year.
Keep in mind that i9 chips below the 7900x have 28 PCIe lanes.
With simple builds, that isn't a problem. 
With more complex builds (multiple M.2 Ultra SSDs, etc), 28 PCIe lanes can be limiting.
The 7900x and above provide 44 PCIe lanes.
 

Thx...lots I dont really understand all in the responses...so thinking; "isn't terribly slow" gives me so more use. As said, not really having issues. Thx again

I am still running a 3770 in an early 2012 Dell XPS 8500 with no real problems with a hobby load. Other than having to replace the power supply, I upped the memory to 16 GB and replaced the video adapter (BSODs under Win10). The latest Win10 update (Fall Creator's) works no problem (except reauthorizing the Addictive apps/VSTs). No complaints. 

I WAS running an older Pentium 4 and it was chugging along ok.  But my current system is light years beyond that one.  I can do 35 tracks and 12 virtuals....and no issues.  Lots of plugs too.

If you really don't need more CPU power, you should invest in SSD drives, at least for your Windows & Program Files.  Best hardware upgrade I ever did.  Check out your performance monitor, and if you are not maxing out your CPU or RAM under a typical load, your system is probably fine!
 
When I swapped from a spinning drive to SSD, I was blown away by how much faster my system booted and started Sonar, opened projects & plugins, etc.  Like a whole new PC!!!  It seemed like any perceptible lag in the UI was eliminated.
 
My Cakewalk content, and VST sample libraries are still on HDD, but I do have my Cakewalk projects and audio folders on the SSD.  My plan is to archive any projects with audio not being worked on onto backup drives.

If you really don't need more CPU power, you should invest in SSD drives, at least for your Windows & Program Files.  Best hardware upgrade I ever did.
 
+1 to this - just done this myself and it has made a massive difference to my system which I think is about 4 years old now - it was starting to creak a bit but now performing brilliantly
My system from Jim Studiocat
i7 2600k @3.4GHz, 16Gb ram, 64bit running windows 7
 
On our new project that we are just finishing, some tracks ran to nearly 100 tracks with a lot of plug ins! - before the change to SSD was really struggling but now, no problems
 
Nigel
 
 

I think we have gotten past the point where the CPU, RAM, and motherboard is the typical performance bottleneck.
 
It would seem to be that storage media would be the biggest limiting factor today.
 
I would also mention GPU's but we're not gaming here, so never mind...

Track count is determined by disk-speed.
Disk-streaming polyphony (from sample libraries) is determined by disk-speed.
EFX count is determined by the CPU.  Having faster drives won't help in this regard.