First, welcome to the board.
Next, you are in luck Mark. I just left a pipeline job in that area and know of some people who would very likely be willing to help you on your quest. Also, you are on a gold mine of a message board for VERY valuable info. I suggest the same to you as what I did and what most everyone here will tell you to do.... Read, read, read. Use the search function for any topic you can think of. Randomly read threads in the tech sections. If it exists for these cars, odds are there have been threads discussing it. This is a fantastic community of people, possibly the best I have seen in the car hobby. Most everyone here is extremely helpful and polite to boot.
Some fellow GN/Turbo Regal owners in your area I know are as follows:
Bob Speiser (Bobs rare 6) -
http://www.turbobuick.com/forums/members/bobs-rare-6.html
Mark Parks (Mark Parks) -
http://www.turbobuick.com/forums/members/mark-parks.html
Ty - (JOHNDEEREGN) -
http://www.turbobuick.com/forums/members/johndeeregn.html
Bryan - (Quick6'n'-K.C.) -
http://www.turbobuick.com/forums/members/quick6-n-k-c-.html
I've hung out with Bob & Mark many times. Both are GREAT guys (with really nice TRs). Ty I have talked to in PM here on the board. Bryan I have never met in-person, however Bob says he is a cool cat, too. So he must be. There are some other people in the KC area on the board, but I suck with names and these are all I could come up with at the moment. I met another guy named Matt who has a TTA & a GNX clone (along with some cool old-school Firebirds), but I can't locate his screen name.
Anyhoo, I'm not too sure about the fist two cars you have looked at. My gut reaction says they are priced too high, especially the 100k-mile car.
As far as the textured area on the lower part of the car, it is on every GN I have seen, although it might have been an option. However, I am not 100% sure of that.
Now, to steer to you to a potential car... Call Greg Daughters at VIP Custom Cars in Polo, MO. His number is 660-354-2602. I last spoke to him about 3 weeks ago and he had a 1-owner, totally stock (as far as he knew) GN he had acquired from an older gentleman in the KC area. When last we talked, he was looking to get around $14k out of the car I think. I never got a chance to look at the car, but I remember seeing it on eBay and it looked REALLY nice.
Also, look over the classifieds here. There have been a LOT of nice cars hitting this board lately and they have been priced very right.
So how do you like that Charger? The Superbees are some bad ass rides. What color did you get?
Good luck with your future GN. Hopefully the info above will help with what you're looking for.

Damn! THAT is a sweet car!