Well, here's a NADA guide link - as far as I know, these prices are used mainly for insurance-company valuation purposes and not for resale:
http://www.nadaguides.com/Motorcycles/1 ... 175/ValuesSince 2006, I've seen maybe a dozen MR175's actually sell on eBay, and the prices for the ones in similar condition to yours were usually in the 'Good' to 'Very Good' range, although I think I saw a '77 sell for more.
I'd keep an eye on this auction - it may seem unrelated, but in my opinion it's very much on point:
http://cgi.ebay.com/ebaymotors/1976-Hon ... v4exp=trueI've heard many MR175 guys express strong interest in the MR250, so I wouldn't be surprised to find the same people who might pay top dollar for your bike watching this 250 auction.
Why not list it again on Craigslist and see what happens? You can't stop the lowballers, only list it as "price firm" and then ignore them. You could also reach out to the previously-interested parties if you still have their contact info; even if they're no longer in the market, they may know others who are.
Ray