In this particular case, HLE is something I can afford.
Huh, there are a bunch of arcade boards supported in MAME that are either priceless due to being unique prototypes/location tests, or are roughly the same cost as what C65 protos go for at auction. Fuck it, we should just HLE those games too, right?
If I wanted to write a program that emulates one or more such boards, I'd consider the following:
1) nobody would write software that exploits the design flaws of those boards
2) the result (getting their existing software to run) would be the same, if not more elegant (due to bugs not being emulated and the entire game code being processed at a higher level of abstraction)
3) portability of the emulator would not be affected
and then I would come to the conclusion to use HLE.
Note that I never said that you should, just that I would. And of course, I would not even try to submit my code to the MAME team, because it would never be accepted. I would just make my own emulator instead.