I do the same with my 558s, and not all that uncommonly also wear them to bed, because while I may want to fall asleep to Beethoven, I doubt my neighbors do.

I've been told that from an audio standpoint, the only difference between the 558s and the 598s is the bit of foam stuck to the inside of each can on the former. Supposedly removing this foam improves audio quality, although having done this with my home pair but not my work pair, I can't say I have noticed any difference other than perhaps that ambient sound is a little easier to hear without it. I also haven't noticed any difference between my 558s and a pair of 598s I once had the opportunity to try, thanks to a former manager who had a real thing about one-upmanship. So I'm not sure quite what you get for the extra $50 other than style. (Though the 598s are very stylish!)