I have changed keyboards a lot, as most know. The timing of when to buy and when to sell is crucial. A LOT of people don't know how to buy gear from sources such as Frank. I have often played a keyboard for a year or so and sold it for as much or very close to as much as I paid for it. I've even sold keyboards that I really liked because the time was right.
Because of forums such as this and PSR Tutorial the word is getting out, but I still know of a lot of people who gladly pay full MAP price for their gear. And I'm glad they do.
If you keep it too long you may not be able to get a good price for it. You also have to be aware of when new models are about to come out because that can quickly drop the value of an item.
I almost got caught once a couple years ago in that trap. I had sold my PA3X to buy Ketron SD7. I had to buy another PA3x quickly because I couldn't rely on my Ketron. A week later the 4X came out and I couldn't return the 3X for what I gave for it just a week or so earlier. I got lucky and was able to sell it to a friend in Mexico. I did lose money on the SD7 because AJ would not take it back after I tried to use it for several months without success. But I was able to sell it too, losing only a couple of hundred dollars because they were in short supply. I'm sure the buyer was happy once they finally got it updated properly. If you are playing at home and it crashes, no problem; you just turn it off and back on and wait a few minutes for it to reboot. You can not do that on the job. It has to work every time, every night.
Well this turned into a ramble, but the point is that there is always more than one way to look at a situation. I enjoy using the latest, greatest tools of my trade and can nearly always find a way to justify it to myself, and I really don't care if it pleases anyone else, other than my sweet thing of course. She understands. Mostly. The PA4X is sneaking up on its third year and sweet thing has been around for 37, so it's all good! Think I'll keep 'em both.