Teach,
You need to understand that when a dealer tells you they inspected a coach this old, they basically looked to see if anything is missing. You WILL find things that either don't work, are worn out, or break shortly after purchase. Same thing with the private party sale. In either case, the onus is on you to discover the true condition before purchase. Given the age of the coaches you're considering, condition is everything. If they both appear to be in the same overall condition, their "street value" is probably about equal. And as old as they are, they're both likely to need the same types of repairs/refurbishing. As for the fiberglass, if it hasn't shown any signs of delamination by now, it's probably not going to.
Dealers appear to be playing on current gas prices and thinking that high demand for pop ups makes them golden. There's a 2001 260RD out at Rowley White on Apache Blvd. in Mesa. It's in good overall condition. But checking it out thoroughly, I found at least $1,500 I'd need to spend to get it road ready and presentable, and that's just the stuff I could see. No doubt it also needs brake service, dump valve seals, toilet flush valve seal, etc. And it'll need the gas bottles either re-certified or replaced. Either of the coaches you're looking at may well need the same things, and it all costs $$$. It has newish 225 wide tires on it (should be 205) that rub the frame. They likely tossed those on, 'cause that's what they had lying around, to replace tires that were badly age cracked.
The dealer said they inspected it, and it's good to go. Don't bet on it. NADA as equipped is $5,500. They want $8,000. How badly do you want to own a Hi Lo? Badly enough to pay more than retail value, then dump another couple grand into it? Be careful with these characters. A private party may be more flexible, if no more truthful.
Stu O