Morning Ian... I think you've raised a very interesting question/topic, I know when I built my XBR cafe racer I had approximately £4000 in it when it was finished. I'll most likely have a good £3000 in the tracker when that's done too. However, I personally didn't /don't do them to make money. That by the same token doesn't mean if someone offered me more money for them I wouldn't take it, I probably would😁😁. I again, personally think as you say, a bike is worth what someone is willing to pay for it at that given time. I know I've mentioned this before but back in 1990 I bought a totally standard laverda jota for £1500. I then sold it a year later for £3000, if I'd have kept it, it would now be worth in excess of £20,000 but would it be worth £20,000 I don't think so. Especially if you ENJOY getting out on the bike and enjoying it for what it is... a motorcycle and not so form of bank statement.
I would love to hear some more comments/feelings on this topic as I really do think it's an interesting one, with no "right or wrong" answer ultimately. Cheers, Michael