Depending on your need for power a base boxster is lacking at least for me. I bought an 03 base back in 09 still have it. Initially it was quick considering I was coming from a pickup truck that's not a stretch. After some time behind the wheel the power seemed to be lacking. I bought a guards red 06 Cayman s last year and the difference is night and day. The Boxster is sitting in my warehouse and I have maybe put 500 miles on it over the last 12 months.
I would highly recommend a S if you can find it. The boxsters are wonderful cars but from my experience most people like the extra power an S gives over the base.