1500, I want some of what your smoking
. This car looks like the day it rolled of the showroom floor. I could replace all the guilds, tires, hoses etc for a $1000 and drive it pretty much trouble free for years. If that all these cars are worth why the following, seems like there's no reason to put money in them if they have a $1500 value with basically no mile. No smoke on startup, the car has been started and driven short distances once a month, it was just put away and forgotten.
There's a following because they are an excellent chassis with very good handling characteristics. They're comfortable for a long distance drive while still having the ability to go around corners very well. They are not without their issues, door hinges, small brakes, tendency to warp the rotors due to the small brakes, and lack of power stock being some of them. But having driven many different cars, including Mustang GT's of a similar generation, they are excellent cars. My enjoyment of them doesn't give them any extra actual value though. They give me warm fuzzies inside, but that means nothing in the real world.
As you said, they're not collectible. They're hard to get performance parts for if that's your desire, the year you have is known to have valve guide leakage issues, etc.
If you want to pay $6000 for a 21 year old car just because it's got low mileage, that's your money and your prerogative. I paid $3000 for one with no rust, faded paint, a PI swap, and lots of the suspension and driveline mods I'd have done myself and I feel I got a great deal. There's a guy with a 32V Mach 1 motor swapped for sale for $2500 which I think is also a great deal. Low mileage being what it is, I don't think $6000 is a good deal on it, but that's my opinion. I'm not going to bash the car, they're very nice and I know you'll enjoy it. Just not what I'd pay for it.
97 Thunderbird LX (The GT Bird)
PI Swapped NPI motor with some port work on the heads, PI cams, 80mm MAF, CAI that feeds from fenderwell. Jmod, 3.73:1 TL in Mark VIII carrier, Mark VIII aluminum LCAs, 93 Mark VIII driveshaft, PBR brakes (soon to be Cobras), 18x9 wheels, 255/40/ZR18 Tires, Front and Rear strut/shock bracing, GR-2 shocks, Eibach 1.5" springs, 1989 SC front and rear sway bars.