I get you on this bit particularly. I hit 40 this year and still do the same stuff to a greater or lesser extent than I did twenty years ago. However, there are a number of things I still want to do in life that need a lot of fitness and that basically gives me another ten years to do them, max. I'm not sure it's a mid life crisis in the sense of going and buying a fast car because, like you, I've always had stuff like that. It's more the time and memory/achievement making side of things which is beginning to lurk quite loudly.
The bike collection one is interesting as it's amazing how your motivation can ebb and flow with things you're really passionate about. My motivation in the first place has been a little different to yours as I've been rebuilding the bikes I once had as memories to hang on a wall. Some was bought at decent prices while other things, like the M1 frame, I definitely paid post-Covid prices for. But what I actually want is the big workshop to be able to have all the toys together in; the bikes on the wall, the cars and work bay below, the bikes I actually ride and the kayaks etc all within easy reach. But then I also find myself coming back to the time thing; I work on my own cars and would like a better space for doing that, but then I just recently finished spending about 500hrs restoring my Impreza and while I enjoy driving it, I feel like I spent too long not driving it and the magic has gone a little bit. I won't sell it, but it does make me question whether I really want to go down the route of building something else. Perhaps with the right space and the ability to just potter at it with an hour here and an hour there I will, but then I find myself also questioning whether the ability to do that is just a distraction from other things I could or should be doing.
Another, possibly closer, analogy is that I collect 1/43 cars and 1/50 trucks (yes, I'm a dork but so are most people on here so shush). I keep looking at all the stuff I have in the cabinets and think 'why don't I just sell all this?', but then I do still also find myself looking at them happily as they're in the corner of my office, and they rekindle childhood memories of seeing things rolling past, or from watching BTCC and world rally. And I might have actually gone in the opposite direction after Truckfest at the weekend, oops. But at what point do you let go of the past? Do you have to? I think any form of collecting is a bit strange, a bit unexplainable sometimes, but then if it makes you happy then what does it matter? If you don't need the money, don't need the space, then I'd just shove some sheets over the whole lot so it's out of sight for a while. If in 3/4/5/6 months you'e not been tempted to take a peek, or get one of them out for a spin, then perhaps that answers whether you sell. Only you know whether you'll regret letting them go now vs later if the Spain move comes together, but then never say never, my mate's been planning to move to Canada for the best part pf twenty years and never done it, nor is the opportunity likely to now happen. Would you feel a sense of regret getting rid of them now and then it being ten years before Spain happened, or are you able to draw a line under it once you've done it and not feel like you've done the wrong thing twelve months down the line (I'm excluding financial gain here as you've said you don't need the money)?