Hi Ben,
I don't think it would be a bad thing to have arguments in a subpatch, but I can see little reason why you would do this rather than using an abstraction. (other than being able to stick everything in one file, but if you are writing a subpatch that needs to tune itself to the circumstances than why not make it abstract enough to be used in other patches?
i program quite a lot (either with programming languages and patcher-like systems) and it's my experience that one often needs to do quick and dirty things instead of taking the time to design a reusable module. I find my project folders cluttered with abstractions that i just needed to encapsule a part of a patch - i think i'm more a supporter of self-consistency. I don't say that there is a real necessity for subpatcher arguments but it's probably another level of flexibility.
good gain, Thomas