I'm confused... when did anybody suggest a "workaround"? It seems to me that pretty much the only way to have 2 clients running on your machine is to install at least one of them outside program files.. this has nothing to do with the scripts, but the limitations of a centralized data storage in windows. If you're going to install one outside of program files, you might as well install them both outside program files. I don't see it as a workaround, since there's no rule that programs have to be installed there in the first place. It's simply a suggested default location.
I think you're exaggerating his response about script issues. I'm pretty sure he said that in passing, and didn't mean for it to be the centerpiece of his argument against Program Files. If the script can't handle paths with spaces, or puts data in the $mircdir, it probably has other problems that you'd want to avoid as well. I don't know many scripts like that-- and scripting sites (the good ones) usually reject scripts that store data in $mircdir for this reason. The issue against Program Files\ is much simpler than obscure scripting failures, though, as he said, it makes life easier *if* you happen to have any of those scripts. It's the same reason that Windows ports of many linux programs tell you to install their programs into a path with no spaces, like the infamous C:\cygwin, for example. cygwin should (by now) work fine anywhere else on your machine, but just in case, you'll be better safe than sorry. Installing cygwin in your root is not a workaround for known bugs, it's simply mitigation for potential bugs. The argument works the same for mIRC, and pretty much any program that may eventually run into those pesky path issues.
