To answer your question though... In guitars, no... size doesn't really matter. Since you're ultimately creating music which is an art form... What you use to make it isn't as important as the outcome. As long as you get the tone that you want and are comfortable... go for it.
Size does affect the tone though... The bigger the acoustic, the bigger the sound... Bigger acoustics project better and are great for mic'ing. If you opt for a smaller acoustic electric it's not going to be much of a factor whether it's big or small if it has a piezo pickup...
But you'll notice that a lot of electric guitar players that do some singer songwriter type stuff use guitars with more of a small classical body style... Like Eric Clapton and John Mayers respective signature guitars from Martin... I plan on getting a Taylor 310 as soon as my funds will allow it.
