''So, Are very well prepped race cars still desirable in the Porsche world? ''
Yes, they are. Especially if your running with the right crowd.
For example have you seen some of the cars accumoto has been building over the last couple years?
Beauty From An Unexpected Place - @FlatSixes - the blog about Porsche
I run my 930 track car at road america regularly and good prep'd cars are definetly in demand here.