Thank you again, everyone.
I tested out the 04 base yesterday. I could definitely tell the difference between the base and the S that I drove a week ago (in acceleration, braking, and in the quality of the stereo system -- however the base was still a fun drive that I could certainly live with).
The major pluses of the base car were the low 18k mileage, the apparent good condition, and the fact that it is certified with a 60,000 bumper-to-bumper warranty expiring in July 2010. Not bad for $30k, but I have to decide if I want/need to spend that much. The S has the additional oomph and fun factor and $5k less in the asking price, but no warranty...
I think the advice to take my time with this and not feel rushed is key... It's snowing here (ugh), so I'm unlikely to do more test drives this weekend. Perhaps I'll schedule a PPI sometime next week.
Jen