No stages downtown, alas, but the Festival will continue Sunday if you're up for leaving a little later that day.
UL, Girard Park, and the Downtown are all close enough to walk; you could actually walk from the Festivals to the football game if you have about 40 minutes (I live by the University, once walked to the Cajundome, it was a very nice evening.)
The Downtown is tiny, you can walk from one end to the other in about 15 minutes, but lots of bars & restaurants. Just walk up and down Jefferson Street. Funkiest/coolest nightclubs are the Blue Moon Saloon; Artmosphere; and Grant Street (if open). Don's is the original Cajun restaurant, but it's not my first recommendation. Bonnie Bell's isn't open most weekends, but that is outstanding food. The food at the Filling Station is pretty good, one of the best burgers I've had. Pamplona is the tapas bar, not bad. Athena is Mediterranean, I don't think they serve booze, but if I remember they'll let you go next door for wine or beer. Couple of Sushi bars, Tsunami & Bonsai, both good, a bit pricey. Also, check out Carpe Diem, the gelato bar. Lady who owns it is from Italy, excellent stuff.
Be careful wandering too far off the beaten path Downtown, we had a rash of muggings in the past, although Lafayette's a pretty safe town. We'll take the kids down at night for ArtWalk and stroll around. As long as there are other people around, you're fine.
And when you're at the Festivals, walk over to Cypress Lake on the UL campus, it's maybe 5 minutes away. Just gorgeous.
Oh, and Friday evenings we have Downtown Alive http://www.downtownlafayette.org/ which is an extension of the Festivals: http://www.festivalsacadiens.com/music.html