Sorry, Im jumping in on this one a little late, some opinions I thought I'd share:
1. I had a car with a moonroof once, I liked having it so much Im having one installed in my 02 SE. (~$1,000)
Hold your comments on #1, there is another post open on my sunroof endeavors if you want to chime in: http://www.bonnevilleclub.com/forum/...ghlight=#85586
2. You may run into a snag replacing the factory radio on any of the 2000+ year models, becuase of the "gm-link" system integration. There appear to be two differnt types, one with a ribbon cable (where it will be expensive to install an aftermarket HU and usually involves DUAL installations of both the factory radio (in the trunk) and your aftermarket radio) the second is the non-ribbon cable, where at the least you will lose your door chime, low gas chime, headlights on, etc..Not a big deal, I did it.
3. I agree with previous comments, you can always add a radio, rims, heated seats, etc. One of the hardest things to add would be a sunroof, and after you add it it stays with the car (unlike the rims which you can take if you get rid of it).
4. If they wont budge on the price, milk for freebies. Extended warranty, floor mats (if it does'nt have it), detailing, and at the very least a free tank of gas and pontiac polo shirt.
Good luck, and let us know which one you get!