Tim...
Smart man! If you are happy, don't mess with it. I agree that you may get some bang for buck replacing your CD player, however, I wouldn't just jump on anything. Decide on units you are interested in trying and wait for one to come along at a fair price here on A-goN. If you end up feeling it doesn't provide enough value for the incremental price difference over your NAD (if you sell the NAD), resell it on A-goN. You can likely sell it for near (or exactly the same) what you paid for it, maybe only minus the shipping cost.
I've done this many times and have ended up trying lots of different stuff in my system, for not much outlay.
Enjoy,
TIC