If I were looking to buy a used sled.....whether it had studs or didn't have them wouldn't matter much. If it didn't have them and I wanted them, I'd put 'em in. If it had them and I didn't want them, I'd take 'em out (I concur with the others who state that taking them out won't hurt the track -- some guys port their tracks with much larger holes with no ill effects). BUT.....I could see where some buyers might think that somebody running studs is a "Ricky Racer" type and may have ridden the sled hard, thereby making said buyer shy away from it.
Just a theory.