I often play e3, e5 and ne2... then fianchetto the bishop to g2, and later in the game you can break the pawn-chain with c4. made a very good score with this opening. I developed it 1 ago, when I played against my chess computer, he allways fell for it. but I don't think this is a good opening to play against higher rated players. I once played it versus a 1950 and got a draw, I had then an elo-rating of 1550 (now 1890).
Could 1.e3 be a legitamate opening?

French defense reversed. Why not ? You dont maximize your possibilities to get an advantage by white. But as a surprise weapon ...why not ? I did beat a rather strong "theoreticall nerd" player with 1.c3 Caro-kann reversed once.
All this talk about Miles. He rarely played 1.e3. Again, the GM most associated with 1.e3 is Pavel Blatny. Pavel Blatny has been one of the good guys on the chess circuit, and yet he's totally ignored. I'm surprised to find he's not even listed in the English language Wikipedia.
Blatny's been playing chess since the 1970s and has been a regular participant in open tournaments in the US as well a slew of European tournaments. Ok, he never rose to the highest levels of chess, but he aint a fish.
I just brought up Miles because he could play "give away the advantage of the white pieces openings" and still do very well with them. He was often more interested in just getting a playable position for the middle game vs. an opening advantage. Blatny is a very interesting and strong player - Duncan Suttles comes to mind too. Spassky said that in the opening Korchnoi put all his pieces on the wrong squares, and then put them on the right squares in the middle game. It's late at night and I'm just rambling but I think my point is that passive or unorthodox openings like e3 can be effective with the right player.