Agreed with whats been said. Would definately play with the pan.
One thing to try is delaying them. Double your tracks - so you've got 2 piano tracks playing the same thing and 2 guitar doing the same thing (I mean carbon copies, not different takes). Pan each hard left and right. It shouldn't sound any different to normal.
Now delay 1 of each instrument by, say, 30ms, but on opposite sides of the mix - for example:
Track 1: Piano Paned hard Left, 30ms Delay
Track 2: Piano Paned hard Right
Track 3: Guitar Paned hard Left
Track 4: Guitar Paned hard Right, 30ms Delay
This will give the effect of each instrument being seperated in the mix on each side of the sound stage, but not in the same way as being panned. Try playing with the delay time. Take it right down low (0.5ms) all the way up to high settings (100ms) and see what it sounds like.
Try it out, if it sucks then just ignore me

. I like the way it sound in my mixes, but its personal preference.