[mikefocke]

Tasteful low key mods like pulling post-'03 lighting into a '01, a plus. Deambering a plus.

Litronics and glass window top well fitted a big pluses worth perhaps $500 and $250 to me if I'm buying

Aero kit, spoilers, zeintop all minuses to me.

Engine mods...it all depends who did them and are they for reliability (IMS, RMS, spin-on oil filter, drain plug, etc) or for "speed". The former would be pluses and could total $6-800 in added value to me.

Headers, mufflers would be a big question mark for me. Did they add or detract from the driving experience? Help or hurt the MPG? Can you live with the sound for hours? Hear the radio? Talk with your friend in the other seat? Not too loud if you value your ears for later life. Zero value to me.

Suspension mods I'd have to try them and see what my ride impression was. Do they go over speed bumps? Probably wouldn't pay extra.

Wheels...nice 17s or 18s could be a plus if to my taste, if not a big minus. 19s would have me not even look at the car. Great new tires could be a $500-600 plus.

My personal car is not exactly stock but there are no mods that would not appeal to someone who wanted the classic 986 look. None but the most knowledgeable would know they were even done.

Note that in no case would I value the mod when buying a car at what the mod cost to do. I've seen 10% cited as the typical return on investment. And some mods detract from the saleability or received-price of the car! Just as some colors are more desired than others.

Each persons opinion will be different.