Spending money = spending money, it does not matter if you buy the gear using your mined btc or you sell your kidney for it, also the fact that you will never get your btc back is not certain, if btc price was to drop, then it would be a better option to have bought a miner than simply hodl'ed bitcoin, the best would be keeping fiat in that case, but if you do that and prices spike, you will have to pay more for gears and well as btc, so really it's a game of luck, so balancing between keeping cash, btc and slowly upgrading to more efficient gears is the way I like to play this game.