I agree with dirty_bass 100%

Removing things you dont want is the only way to really clean up our mix. After all a gardener doesnt try to plant more flowers to cover up the weeds, they remove the weeds so they can see the flowers.

The other older addage is "you can't polish a turd." Its no good trying to master a track that contains mis-matched frequencies, amplitude snaps and pops etc etc.

As for mix widening try this trick

(making sure you aint widening anything below about 400hz)
take a loop and clone the loop onto another track, pan hard left and right, invert the phase on the right hand loop and then take away the mid frequenices using an EQ on the left. experiment a bit with the EQ and you should be able to hear bits of the loop pulling backwards and forwards.

HTH!