"I've read the 2.5 isn't worth putting money into" ... none of these cars are 'worth' putting money into if you expect to get it back, but it's your car and your money, you can put it where you like!
"I'd like the clear LED headlights. Likewise the taillights." ... the aftermarket 'led headlights' are not generally that well respected on this board, you'd be better getting some new/used standard clear headlights and fitting a xenon kit from Nine8Six when he starts making them again
http://986forum.com/forums/diy-project-guides/48169-porsche-headlight-retrofit-%5B-cad-prototyping-finish.html ... or just a generic aftermarket kit.
The aftermarket rear clear lights in various designs (eg Depo) you can pick up for a couple of hundred $ on ebay etc.
I'm pretty sure I've seen quite expensive LED 'kit' somewhere... but the interiors you can just buy generic leds in the right sizes from ebay and replace them, shouldn't cost more than a few $
So, how did you do the interior ambient lighting, been thinking about adding that to mine?
Other things I've done in my 2.5 as inspiration ... double din head unit with navigation, short shifter, led shifter knob, footwell lighting, replace top with glass version from 03 model, variable intermittent wipers, remote central locking.