I'm sure you already know the faster it goes the more time, maintenence and money it requires.
Decide how much time you want to throw at it first. The you will know how fast to build it.
I've had three Turbo cars now and my mid 12 second "stocker" was probably the most fun. Ran forever with nothing but ordinary maintenence.
My present T with the new motor, trans and turbo should easily push into the 10.70's but she is requiring more time and money now than I have to give her.
I would now rather spend the time with my kids and their sports, horses and drive one of my cruisers than be under the hood of the T (time to sell it while it is all new and go find a mid 12 sec car again).
I say keep it mostly stock inside and out, but put a ton of go fast goodies in the engine, aftermarket exhaust, etc. But don't tub it, keep the interior mostly stock, keep it orogonal color, etc.
I say leave it the way it is. Looks like a good survivor to me. I've had some pretty nice ones over the years but it's just as rewarding to have one that isn't too nice to drive more often.