I've done a few meets recently in retired road running shoes (~300 ish miles on them), and it was less bad than I thought it'd be - probably makes a big difference how many wet logs and wet / loose / steep hills, plus I haven't tried it fit so power hiking in the worst bits anyway. It sometimes makes me think how I spend so much time thinking about o shoes, gaiters, thumb compass, clue sheet holder, etc. and their combined time advantage is less than I lose to any mistake!
AR is similar - once when I'm in shape I think it'd be funny to do a race entirely equipped by local box store - have a total equipment bill less than many racers' rear wheel hubs and beat 'em all anyway.
Definitely prefer the right shoes of course!
The only good thing about a messy car is that I often have spare gear available to me that I wouldn't have otherwise. But I need to just buckle down and start actually planning ahead and preparing better like normal people.