Actually depending upon the engine they are extremely easy and cheap to fix and even add horsepower to.
I raced cars and the rule of thumb was to "freshened" engines every 100 hours or so, basically rebuilt.
Learned a good lesson racing, spend your money once, do the job right with the right parts. Did this for 40 years and after wasting about 6 grand
and blowing up 3 I spent 3500 and built a good one, lasted 6 years and was still running when I sold it, DYNOed at 587 hp. Didn't have to freshen that one more than once.
Inboards are cheap, cheap ,cheap. Easy to repair, just about every mech can do it but racers do it right. There is a lot more car mechs that can do this than boat mechs.
Someone posted asking about Canada Engines, not sure now but there is a big difference between an engine for a car and one for a boat, just types of parts but not much difference in price. And metals are much better now. Much cheaper too. So they are probably okay. A stock Chevy V8's red line is/was around 6000 - 6500 rpm.