G'day Bluesman - I'm writing from Australia as if you couldn't tell!
For what it's worth, I use a similar product to Cool Edit Pro called SONAR XL (arguably a dash fancier in some areas which don't concern you) and yes, I used to notice the same thing until I invented my own solution. It's a nifty trick which you could probably do quite easily within Cool Edit Pro too.
Firstly, you'll need to buy some top flight "Mastering Plug In" software for Cool Edit Pro to be able to do this. Take note that obviously, such software is nowhere near as 'top flight' as a dedicated 'mastering house' with $100,000 of dedicated outboard hardware, but products such Steinberg's "Loudness Maximiser" and "Timeworks Mastering Software" are pretty bloody good! Believe me!
Anyway, what you do is this - you create an interim "Pre Mastered" directory where you dump your initial mixes. Keep doing what you're doing now - you're doing the right thing - you're keeping your work well below the 'clipping line' and this is good. Just dump your initial mix in the pre mastered directory in as high a quality format as possible - that is - in 24bit if possible and 88.2Khz if possible - that sort of thing. You see, even if your original project is only in 16/44 you still lose a little bit when you mix it down - but you save some of that if you mix it down at 24bit and at higher sample rates.
Then, within Cool Edit Pro, create a 'Final Mastering' project which does nothing but load your 'initial masters' from the pre mastered directory.
Here, in this file, you then implement your mastering software and tweak your volumes the right way. You'll find that some files will play at say -4.5db and others will play at -1.5db - that sort of thing - but it's no worry. What happens within 'mastering software' is that a lovely mix of limiting and compression takes place which can raise your initial master up to the 0db CD ceiling and then you export THAT file as your official CD-R song.
It takes a bit of time to learn the best settings for your 'mastering software' but by and large, with practice, you'll be absolutely astonished how close you can get to the big boys.
One thing though - play a reference album which sounds close to your own song quite regularly - or ears tend to get immune.
Don't be dispirited if you have to go back and remix your initial master and then import that mix once again into your 'Final Mastering' project. It's quite a normal process to refine and refine away.
