Do you look at your collection and wonder if you are wasting money? No. A life's passion is never a waste of money.
they have to be insured and maintained and what if you find you only ride one of them a handful of times, but can't bring yourself to part with it? Yes, and it's worth noting that the one that costs the most to insure, is the one ridden the least, and vice versa. Still don't care.
Is it nuts to have more than 2? No, I have 4. One is a race bike, so 3 are licensed and insured.
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Some time back, the topic of "How many bikes do you have" came up at a VRRA winter dinner meet-up. I had the fewest bikes of anyone there. Ten ... twelve ... but the best answers were "It depends how you count them", and "I don't know".
I will say that all four of mine are in complete, functional, running condition ...