The main problem here is that locals do not live in hotels. When you arrive to some place, it's better to know about opinions of other tourists....
As for bars not full of tourists - if you are not afraid to travel at night in the unknown city, choose local bars

Tourists are usually only in the center of city. I know there was kind of "Big Apple" and "Truna" clubs in Imanta district, as well as a lot of cute caffees on Jugla district... I'm only afraid not a lot of locals are going there. Mostly all beautiful youth is located in the city center.