your current wheels give an impression of being larger than 18's for some reason. personally I'd keep em, and we both know most people here would despise larger wheels than that but it definitely wouldn't look bad
Personally, the ones you have look rugged while also looking sort of pimp-my-ride-ish. some people like rugged steels only, some like a mix and some like pimped out 26" chromes, doesn't mean one is right. Its the same reason different people dress like dweebs, preps and thugs. i like the rugged or mix for myself, but i still think the "pimped out" ones look sweet- just not my style (just make sure your rims never exceed the value of your car)
If you do put bigger wheels on, I wouldn't advise any off-roading. and even if you don't think you want to off road, i'd give it a try. I had a blast my first time, in moab....and wish there was more of it in missouri.