You're right Osborne is a classic. I think this would be an indicator that would have good cross-site appeal on TM. The highest prices often go to the nostalgic non-collectors variety, so perhaps spending some pennies on promoting the auction might pay off. I've never spent upgrading an auction but I have been noticing that it seems marshal in four to five hundred views on an auction.
See 'Dick Smith VZ300 Computer' with nearly a hundred views a day.
http://www.trademe.co.nz/Computers/Vintage/auction-352995421.htmHardly a classic or interesting or even useful vintage computer (thought I might consider it as a spare if the price were to stay the same), but that's a tonne of views which might be coming through from somewhere else. I'm not sure if you can tell by looking at an auction whether they've paid for the cross-site type ads and some of the other extras.
With a wider market, I'd even try my luck at listing the Osborne for $200 as you're now looking outside the penny pinching VC collector for potential buyers. I never really understood how vintage software depreciated so much. Those old Sega carts which only can fetch $5-$10 at times use to cost around $100 each.