Interesting thread and a very good question. As with most things, everyone has their own opinion on the matter and I'm no different. I have done a lot of "buying/selling" of used equipment over the years and owned most tiers of all brands of radios at one point or another until I finally decided which I liked best. In addition to that is all the other misc and related ham shack gear and some classic/boat anchor stuff also. Other than a couple of VHF radios, I have never purchased a brand new one, and regret that I purchased those. I always look for used equipment as new gear is almost always just over priced IMO. Add to that, I normally go with "top shelf/high end" gear and avoid the lower end and basement level (MFJ) stuff altogether.
All that being said, I have always found it interesting how the prices for older/used gear seems stay high, even as newer equipment that in many respects, far surpasses it. I always do a lot of research before a purchase and watch the used market carefully before I pounce. I'm trying to see the "range" of prices on a given item over a relatively close period of time. Doing this I get the feel for what the "going" price is and also spot the low as well as the stupid high prices are. I'm sure most of you do the same.
When I see sellers on the high to ridiculous high side, I figure some of a few of the following is going on. Some of these are normal for almost all pricing, namely #5. Not all of the list below are necessarily a bad thing. Note: These are just my opinions and I could be completely wrong...your mileage my vary.

1. They don't know what it's worth.
2. Are very attached to the item and think it's worth more than it actually is.
3. Just hoping for an unknowing (sucker) buyer.
4. They paid full or a high price when they purchased it and are determined to recoup, regardless of actual worth.
5. Adding in the "bargaining" price up front. (Mark it high...the buyer counters...and hopefully they get what it was worth or more, to begin with.)
6. Just trying to screw someone because they might be able to. Different than #3.
7. Have in there head that the item is now a "classic" and worth more than it actually is.
Perfect Example: Just a few minutes ago, before stumbling onto this thread, I saw a Yaesu FT-1000MP MK5, MD-100 desk mic, "asking price" $1650.00. The mic is a nice inclusion but still the ask is HIGH and I just had to laugh. And yes, I'm familiar with the radio and know all about it. It was THE radio I wanted back when it was new but couldn't/wouldn't afford it. Last year, I did my normal due diligence, watch, wait and pounce routine. I got mine for $750.00. A fantastic price on the low end of the range.
Some gear IS classic, like a lot of the Collins gear, and some gear IS rare, so high prices in these instances is probably warranted. However, the vast majority of older, regular gear, is in my opinion, overpriced in comparison to more modern/capable gear. Of course, as long as people PAY high prices for gear, then people will continue to assume it's WORTH those prices. If we didn't pay, the prices would start to go down to realistic prices. Oh well, one can only hope.

73
Vince N5ATM / HS0ZPQ