I agree with Tim. Some colors the VE3 looks better with than others. Also Some RS cars look better with the VE3 than a non RS with it. I would say it is kind of the lump sum of options that make the car. For a hard core 1st gen guy, it is only documented original items that add value. Regardless of what the insurance company says, it all depends on what someone is willing to pay for the car, not what it would take to restore a car.
I have an early L.A. 69 RS Z. It does have factory spoilers, deluxe seat belts, tinted glass, AM/FM radio and the VE3 bumper. I think the VE3 bumper with the RS package really add to the look of the car, and would help it sell, since there are not a bunch of eye catching options otherwise ( no console/gauges, to early for the ZL2 hood etc)
IMO what helps these car sell faster than others is having docs, and a nice history of the car. Especially where a Z is concerned, since there are so many copies out there. Canadian docs are nice, POP is good, factory invoice(s). The more docs the better.
Someone may be able to fake one of those items, but I doubt would be able to fake all of them, and make them pass muster for an inspection.