From time to time I revalue my coins for insurance purposes. I also compare market/retail value to cost. Needless to say - and quite apart from the pleasure I get in them - my coin collection is far from my worst investment.
Yes, it's each to their own. Personally I would sooner have a coin than a flashy car, but for others a car is more desirable. Some people spend thousands on a holiday. The market in used holidays is quite stagnant at present - at least a collection is something you can resell.