In reply to mark k..

I wrote a licensing manager that was e-commerce-plugin agnostic, because I didn't know at that time what bit of e-commerce software I would be wanting to use a few years down the line. Moduralisation is good.

As it is, I've never used EDD. I have no opinions on it either way. For me, the answer to lots of "why not use X instead?" questions is "because what I'm using works, without any known side-effects".

How many plugins you have installed on a site matters very little - much less than whether those plugins are well or badly written that makes a difference. Of course, fewer plugins means fewer plugin updates; but, on the other hand, functions that aren't modularised sufficiently cause bigger fall-out when you hit a problem with them.