Yeah, it's been like that for me. Sell one, regret it later, sell another one at a higher price, regret that one too...
A couple years ago, I came up with a personal rule that basically says, "If a set rises fast off the blocks (retirement), hold it longer, 'cause it will likely keep rising". And vice versa. The 'vice versa' part (if a set rises slowly post-EOL, dump it quick, 'cause it's probably going nowhere), has stayed true for the most part. The problem is, over the past year, several sets that initially rose rapidly have then slid back down.
Holding 10211, 10221, 10224, 10225, 10228, and 10937 for the past 12 months has netted you a loss. All those sets doubled (or then some) very fast post-EOL and then got stuck. 10228 and 10937 have fallen sharply since then. 10937 actually hit $300 in a couple months after EOL, and then dropped down to $250. That was long before the remake was announced. And of course there hasn't been a remake of 10228, or any of the other sets I mention. So I'm not really sure what to think any more. There are ceilings that sets hit, even without a remake.
I'm regretting selling my 75054's too fast this holiday season, and to a lesser extent my 75055's. But I'm really glad I dumped most of my 10228 stash last Fall at ~$430, 10225 sets at $360, and so on, 'cause those have only come down, and sitting on all of them for an extra year only to tie up my funds and floor space for negative returns would have been pretty terrible. For these newer sets, there's a lot of shadow inventory out there, folks just waiting for the price to plateau so they can back a truck up to an Amazon warehouse and dump their stash into the FBA market. Ditto for eBay. So for example, the number of 10228 sellers on eBay has actually risen as the price has come down. Happened to 10240 as well. It would be great if there were an online inventory tracker measuring the number of sets sitting in garages, basements, attics, and whatnot, but all we have is self-reported measures, and I have the feeling that the really big sellers don't bother updating the world on their changing stock levels.