The car will turn in easier with a narrower tire up front. The 'feel' of the car is attributable to the compound/structure/tread pattern of the tire; the width (total amount of rubber) comes into play when you're using a significant amount of the available grip. There's not much of a difference in total grip between the widths you're talking about.
Personally I would keep the staggered setup and get non-directional tires so you can swap side-to-side. There's less than a 10% difference between a 235mm and a 255mm width tire. You can run a 235 on an 8" OEM wheel and a 255 on an 8.5" just fine (the latter is factory spec). For the street I run 235/265 on OEM 19" rims.
Should you go square with OEM rims, you may want to invest in some spacers to even out the appearance of using OEM rear wheels up front; it will look a little off.
RFT's work well with the standard suspension. Going to a non-RFT will improve grip (assuming the right tire) but take away some illusion of turn-in responsiveness provided by the rock-hard RFT sidewall (RFT sidewalls have very little flex so it adds to total spring rate).
Edit: Invest in some camber plates if you really want to improve the handling of the car; they aren't that expensive and running -1.5 deg. up front will noticeably improve cornering performance.
2011 BMW E92 335i - Le Mans Blue/Black, 6MT, M Sport package
Last edited by CJ421; 01-16-2013 at 10:45 AM.