You'd be surprised how many old school pro's start their mixes with nothing but bass and vocals....at least in the non-metal world. In certain genre's a lot of guys think it's the lynchpin that holds a track together. In a lot of metal mixes, it's almost an afterthought. Depending on the bass line, it can form a large part of the guitar sound though.
If I remember correctly, loads of the dudes interviewed in the Mix Engineers Handbook (a great read....especially while at work
) mention starting with bass as it's essentially their foundation from which to work. Most of the guys I used to work with started their mixes with nothing but the centrally panned elements, kick, snare, bass and the lead vocal and using this method and a great source track, I don't have much work to do to slide it into a mix.