There is actually a lot to do for a town this size just depends on what you are into.
- Multiple theater groups always looking for volunteers (musical and spoken only)
- Lots of parks to wonder about in. Washington Park especially has lots of events.
- Fairly active running and biking communities.
- Some gym enthusiasts.
- Board game nights at Titan Games.
- Tabletop seems popular with two stores doing Warhammer 40k and Worthwhile/Hordes.
- Definitely some art groups, check UIS for more info on that. I know gallery nights are a good way to get in.
- Lot of downtown mini-festivals should be coming up now that the weather is improving.
- I've seen a number of D&D groups.
- Shriner's club and free masons.
- Lot of bars but I haven't been to them in years so not sure how that goes.
- Obviously the Lincoln tourist stuff is worth hitting up at least once.
- Wide variety of restaurants for a place this size.
- Use to have a good indy/metal scene but I just recently moved back so not sure about that. Black Sheep was the spot to check.
- Good skateboarding groups.
- UIS has some community groups and projects.
- There should be some stuff out on the lake as well but not sure what all.
The best part is, unlike Chicago, you can afford to do this stuff. The biggest problem is you have to go looking for things because the web presence is lacking. Pick up the local free paper at Monties or Headwest or wherever, can't remember the name of it, but it lists upcoming events.
The bar scenes are hit and miss some nights but Thursdays and Saturdays seems to jump up the most.
There are some good bars, however, if you like to drink beer.
Obed and Isaac's as well as Engrained are two local breweries with really good beer. I would say avoid downtown nightlife – it's nothing but trouble, with people trying to fight and shit.
It doesn't seem like Springfield supports original music much – it's not really a big enough market IMO. But there are quite a few local cover bands, and a number of them are pretty good. Maybe not Nashville good, but you might enjoy some of them. There is a music festival downtown the first weekend in June. I haven't been to it, but it seems to be a big deal.
Coincidentally, I'll be in a wedding in Nashville that weekend.
There are some pretty decent parks as well, that are probably starting to have events as it warms up.
There's a highly active disc golf club in town. Four free courses spread out across the city. Its great exercise and you can play recreationaly or with the league. If you haven't tried the drive in movie theater yet, you should! Personally, I'm involved in the theatre scene.
There's a good group of 20s and 30 somethings that hang out regularly and work on shows together and whatnot. Its all community theatre so its mostly laid back.
Hope you find something you enjoy.