I love fancy stationary and pretty papers so I would probably never email invited for something meaningful. However, I remember when typing something, rather than handwriting it was considered too impersonal. Then, for a while, emails were considered okay for business or very short notes, but not for "real" letters or anything important of a personal nature. Now things are continuing to evolve and more and more people use e-vites for all types of situations. I see it as times changing--not as not being formal or informal.
Can you pelase clarify which is it though that you are truly concerend about FORMALITY (as your latest post indicates) or PERSONALIZATION (as prior posts indicate--you said a handwirtten on plain paper "please come to our wedding" type of thing was good--but it is not formal)

I really am getting lost as to which one is the issue for you.