Agree about the ties at the back, just below bust level to pull it in a little - but I think the main problem is the big expanse at top. Would a collar make it look less plain/smock-y
Took the liberty of photoshopping some terrible pix for you
(I should dig out my tablet and pen, drawing with a laptop touchpad is impossible) Standard, cowel and peter pan.
For a much nicer looking peter pan collar see the tute here: http://wiksten-made.typepad.com/photos/peter_pan_collar_tutorial/jennygordy_2.html
(not mine and I've not used it, just fyi) On the peter pan one I have also taken the bottom of the sleeves (gather at the bottom and sew a strip of fabric to give a bottom puff sleeve) in to give a prettier look.
Personally I think it could look quite mod-ish with the sleeves and peter pan collar.