And no offense but you seem to by hypothesizing about the app too much; if you use evernote and need a way to get your SMSs to evernote try it out; if it sucks delete it. Easy and simple.
Frankly if evernote develops an add-on that let's me save SMS directly to the app I'd use it instead. Till then mysms appears to be the most convenient tool for this purpose.
That said, I frankly haven't tried sending SMSs to my evernote email; just didn't occur to me so it sounds worth testing; though I assume I would still need that extra step of selecting then emailing, which I currently don't need to with mysms