Is the rest of the car original, drivetrain? If it isn't, then changing the interior won't matter much to the value when you sell it because the sale is about looks and not originality. It may even help the sale price.
I agree with Austin's prior post... He should keep the orig int or change it.. based on his own likes... and what his future plans for the car are. Does the interior need to be updated, or is the original still serviceable? If he would LIKE the car better himself if he changed to yellow interior, then maybe he should do so.. (Interiors can be fairly easily changed).. but he should be aware that the Yellow (and orange) houndstooth seats are not for everyone... I've heard many say that they couldn't drive a car with such an interior... When I first got a peek at my car's interior (before I purchased it), my initial thought was 'UGH"...
.. but after I thought about how different it was, I began to change my mind... (but I'm a bit odd, as I like to be 'different' from the crowd)..
(and NO, we don't need 20 more posts agreeing with my last comment!)..
PS. A few months after I purchased my 72/720 Z28-RS, I came across an almost identically optioned car (in yellow!) for sale.. only a few miles away.. ($1900)... solid car all there.. I wanted it also!
but wifey put a stop to that thought..