If you wear the kilt properly, up toward the navel, the kilt will fall straight down and look good. It won't hide your belly, but it will look neat. If you wear it too low, like jeans, under your belly, then it will definitly emphasize your gut. It will also look like crap from behind, as the back will be several inches higher (6 or more, even) than the front. As long as the sporran chain isn't too ticht, it should hang ok and look good. On the other hand, you have to try it and see how it looks for yourself. Personally, I think the front of a kilt looks empty without a sporran in it, and I like the convenience of everything being right in front of me if I need my wallet or something.

One other possible plus - I don't think I've ever heard of a pickpocket stealing from a sporran. That would be pretty bold.