I recently asked the same question here and got similar answers to those you've seen in the past.I feel this topic deserves a fresh look. So, what do you think?
Having said that, Buell prices do seem to be quite region specific. $4,000 may buy you a very nice example in some parts, but a pile of junk in others. Asking prices go up to $10,000 where I live but I'm not sure if the owners are actually moving them or not.
If not appreciating, prices do seem to have now stabilized. I recently sold a nice clean XB, 2 years after I bought it, for exactly what I paid for it. Granted, I didn't have a line-up of buyers at the door, but it sure didn't take long to sell either.
I think if you're looking for a bike that'll be inexpensive & lots of fun to own, with a chance of recapturing your initial capital back out of it when your'e done with it, a Buell makes a lot of sense. If you're looking to fill a barn with them for 20 years in hopes of getting rich one day, there's probably better ways to invest.