Avoid chemicals. You don't need them.
I wouldn't recommend using any sort of solvent on the plastic. It could cause damage to the plastic that may not be immediately visble, but could show up later as discoloration or brittleness.
The best way to get rid of the sticker residue (using no chemicals or abrasion) is to use the back of the sticker itself and reapply it and then quickly lift it off in an attempt to pull the residue off (cohesion to the adhesive sticky stuff on the back of the sticker is stronger than the adhesion to the dashboard). Repeat until the residue is gone.
You can do the same thing with simple masking tape. Press it on over the residue and the lift it off quickly. Repeat as necessary using fresh pieces of tape and the sticky residue will soon be all on the tape with none on the dashboard.
