What frequencies does a Limiter booast ?? All of them equally ???

If you need to boost loudness in a mix.  A limiter is definitely not the first place to start.  As was mentioned, taming the bass response is the first step in increasing loudness.  At higher listening levels bass tends to cut through.  Even if you lower it in proportion to the midrange it will still sound just as full once the levels are brought up.  Allowing a "free" doubling of volume without sacrificing overall dynamics due to simple psychoacoustics.  Plugins like maxx bass are popular for mixers because they affect the higher overtones, allowing a sense of louder bass without increasing the lowest fundamental which can then be reduced. 
 
If you are needing dynamic control to boost the level, it is always better to try it first with a standard compressor on the track level, which will offer a much smoother reduction in volume and also allow some transients to escape, keeping the sound punchy. 
 
That is really as far as you should go before sending it to a mastering engineer in a commercial mix.  But if you need to DIY 100%, a master buss compressor followed by a limiter is a good idea.  If the limiter is reducing the transients by more than 3 or so dB to achieve the volume that you want, you really need to look earlier in the mix to see if you can sneak through a few more dB before you set up a brick wall.  (ie.  tame the transients causing the problem, not the entire mix)
 
Contrary to popular belief in the audiophile world, even us classical engineer use limiters and compressors to boost dynamics.  Especially on vocal or piano spot microphones.  It is inevitable in the world of mp3 and noise competition in car stereos.  We just use much lower ratios like 1.3:1 and have a higher standard headroom for dynamics. 

Hi Kev,
 
Well, I'll get impaled for this but I'm not one that really likes to use any limiters on my tracks because I find that they don't allow the tracks to breathe as well. Then again, it depends on the style of music you are producing, but for me, a limiter just about never gets used on the stuff I record here.
 
I HAVE had to use limiters on client work that comes through here that was recorded somewhere else, but nothing I record here is ever in need of limiting really. I'll use compression with automation before I'll put a limiter on something. The only time I may limit, is on a snare drum.
 
For example, I'm using a transient designer on a snare to make it crack a little more. This makes the snare lash out a bit at times. So I'll automate it to try my best to preserve it and not pick up any artifacts. If I still see/hear it lashing out a bit, I may try a compressor. If it still lashes, I try turning down the level on the transient plug. I do anything I can to not use any limiting because as soon as I do put a limiter on, the snare can sound "the same" for every snare hit as well as lose some of its dynamics. Snares as you know are really dynamic yet there are times where we need them super consistent. So when I've exhausted everything, then I'll put a limiter on or a compressor policing things a bit more strict.
 
Now for bass guitar, a limited bass would drive me insane. LOL! I find limiters just suck the life out of the bass in situations where you want it to be a bit more dynamic. Again, dynamics are super important to me, but there are times when we may need more consistency in a style of music. A limiter would probably be helpful, but on my end, I'd most likely never record a bass that would need a limiter.
 
I like to lightly compress my basses going to disc destructively to condition them and keep them a bit tighter during the recording process. Though a lot of guys wouldn't want to do this as they could risk ruining the track with too much compression to where it may need to be re-tracked, destructively recording with a little compression makes the bass a little easier to play and can sweeten the tone up as well if the right compressor is used. So this gives me a totally different bass to work with in my mix instead of one direct right into Sonar that has 0 processing. You just have to know how to go about it...and I've been doing this so long, I get it right 98% of the time without a reprint. LOL!
 
As for the limiter cutting off your highs, yeah you wil definitely notice that. Quick example, you know how people are going for super loud, squashed mixes these days? What you DON'T hear in those mixes, is their original snare drum. The limiters kill snares so bad on full mixes it's not even funny. That's usually the first thing I hear (besides over-all pumping and breathing/squashing artifacts) because the high end crack is removed. This same thing is going to happen in your case because the limiter is going to concentrate on controlling the transient...which usually comes in the form of a high end crack, pop or percussive attack on a bass guitar.
 
So the first thing the human ear picks up on is...the high end isn't there. It's STILL there, it's just that the transient of that instrument has been either softened or drastically removed. Adding an eq like you mentioned may bring things back to life a bit, but it could also create more problems for you because then you may add artifacts that further remove the purities of the instrument you are trying to process.
 
For effects purposes, this can really be cool. But if you are working with instruments that have started out sounding real, you can very easily turn them into synthetic instruments that not only sound fake, but may no longer fit your mix. So you definitely have to be careful. Without hearing what you're working on, it's hard to even tell you what to try.
 
But for myself personally, I try to keep things as pure and real as I can without over-processing with compression and especially limiting. I know some guys have great results using limiters on their instruments. So I'm not downing it, it;s just not something I like to do unless I really have to. Hope this helps man. :) Best of luck.
 
-Danny