The thing about Di2 is that for almost everyone, it is simply a luxury item that one can easily live without. (The exceptions I have in mind are people with arthritis or other conditions that really could benefit from not having to use mechanical shifting.)
As far as luxury gratuitous items go, I really like it. For me, it has been great not having missed a shift in five years. (I developed a lot of weird anxieties after breaking my ankle, one of which was a fear of shifting, probably due to having the chain come off my triple on my old mountain bike more often than I care to admit. Di2 cured that.)