I'm guessing 'GT 248a' is another ay of saying 'GTS'?
It is rare to a point.. Doesn't really increase the value, more of a 'cool' factor IMO. Maybe in like 10+ years it will affect the price point more..
Thats what oi have, its lighter less shit to break and no shitty leather to crack, but no its not worth more because of it, the mileage helps but thats it.
"rare" -- they still made 1000000000 of the 248a's. are they more rare than the standard GTs? yes, but as Ferocious said, they aren't more valuable becuase not many people are into stripped-down models.