I am not a third party member, but I agree that you should vote for the best candidate by your view. The only wasted vote is one which is not submitted for the candidate you truly believe in.
When third party votes increase and cause more ruckus, then they may be taken seriously by the big two and one of the big two will see more fit to reform the system to encompass the third parties into government.
I have submitted a way to give third parties some representation within the system here:
http://www.tfproject.org/tfp/showthread.php?t=69962