It really just depends on what you want to do with it. Personally I would have no use for a dedicated DE car. A DE is non-competitive by design so going faster/ more hp seems somewhat pointless to me. No matter how fast you go, you cannot "win" a DE. You are just out there kicking your own azz. I live for the competition.
If you want to compete in Time Trials or club racing, choose a car with an active class and lots of cars to fill the grid. Boxster Spec and 944 Spec both have very active classes that run nationwide. Both of these cars can be set up with hard tops and full roll cage that protect the driver very well. Running in one of these classes is every bit as much fun as running Grand Am or ALMS at a fraction of the cost but any dedicated race car is a black hole for $$$.
Want to build an unlimited, high HP, TTOD, track car? You will get to share the grid with guys like Loren Beggs in his FrankenCayman. All tube frame, twin turbo, 3.8L, 1000hp, 2000lb rocket sled. His car is a $200K+ development platform for testing ideas that he adapts to racing customers of his shop. Sharing the grid with this beast is quite humbling for even a top driver in a GT3RSR Cup car.
Set your goals first: Track car for kicks and grins, TT weapon for regional/national championship, club racing series championship, etc. Once you have a clear goal in mind the car question is a lot easier to answer.
Most guys that feel they are getting bored with their cars are actually getting bored with a lack of competition. There is talk of a Boxster Spec national championship next year. My car is now fully developed to this class and turning top times. As long as the spacer between the seat and the steering wheel doesn't screw up
I think I have a shot. Maybe we will see you at Boxster Spec nationals in 2012.