There is a lot in downtown Naperville, but not necessarily a lot that meets your criteria. Also, many restaurants have come and gone in the last few years (Bistrot Margot, Samba Room/Timpano's, Clara's at the Square, Masala Yagu, Tessa's, 10 West and its predecessors).
IMHO, Hugo's is the best restaurant in downtown Naperville right now. But, it doesn't offer much (if anything) for vegetarians, and can be quite noisy. La Sorella di Francesca (the first Francesca's restaurant to open in the suburbs) consistently is good, reasonably priced Italian -- it is a good choice. However, it also can be very, very noisy and is extremely busy on the weekends. You may want to take a lot at Raffi's, which is in the 5th Avenue Station building just north of downtown...It may be more suitable, given what you're looking for.
From what I've noticed, the restaurants that tend to prosper in downtown Naperville are high-end steak and seafood restaurants (Hugo's, Sullivan's, Catch 35), bars/pubs serving bar food, Mongolian barbeque places and low-end, Americanized Mexican. There are chains like Ted's, and also a Heaven on Seven, that do quite well, but they are not what you're looking for. A lot of ethnic and high-end (non-steakhouse) places have not been able to make a go of it, for some reason.