I use my retro GT's for a commute to work mostly as I don't want to wreck them by going off road!Hmmm. that's a point. I've not fitted considerably wider bars on any of my GT's with FF stems - a couple around 600mm which are GT riser bars. I've not noticed any issues, but then I don't ride anywhere near as hard as I did back in the dayNot on these bikes anyway!
Mine do see some single track and towpath action and the occasional pump track thrash (much to the amusement of the local yoofs on their sponge bikes) I stay of the quarter and half pipes these days thoughI use my retro GT's for a commute to work mostly as I don't want to wreck them by going off road!