my teacher was a guitar teacher teaching bass, but he used to tell me I was trying to do too much. I remember once he left me grooving over Beat It by MJ. A really simple bassline that you [i]can[/i] throw fills into but don't [i]need[/i] to.
I then realised that fills aren't about blasting out 100 notes per second (though I do enjoy that nowadays), it's about making it sound good at first. Fills involving rests and longer notes, i.e. less busy, will really help you keep the groove of the song. Once you have this down, you can work on the fiddly twiddly stuff for the next x years.
I learned playing along to Muse and Nirvana on CD too, used to get my timing fairly well IMO, keep that up and you'll go far.