There are a lot of dependencies here:
Where is the bike located?
Does it have maintenance records and who maintained it?
What aftermarket parts does it have?
What color is it?
I think others can chime in on the engines, but from what I've read they are reliable and will maintain good compression well past 25k miles with routine scheduled maintenance.
Ultimately, however, "worth" is something that will be worked out between you and the seller. What is it worth to you? If you don't have a price already in mind, then you need to do some craigslist research at what other Bonnies in your area are selling at. Keep in mind that sellers on craigslist often list their Bonnies at a price that is higher than they are willing to accept, leaving room for you, the buyer, to negotiate.
With all this in mind, if this was a clean '02 Bonnie, with complete and up-to-date maintenance records, and with tasteful modifications or none at all, I would pay about $2500-3000 for it. This is for my market, however.
Last edited by luckyduck; 11-06-2012 at 11:33 AM.