IMO unless you have an extremely clean low mileage ride like Lowmile than I really don't think changes will have much impact on resale unless its something "extreme", ie a monster rear spoiler.

The previous owner of my '91 changed the front turn signals and rear lights to conform with late '90's standards and I'm glad he did as I think they look better. I plan on painting the car 1 color next year as I think it is a better look.

Personally, I prefer the 3 vent over the 2 but that said it's your ride. As a wise person on these boards said before, "who cares what others think, its not their car".