What do you gain by voting Republican?
What do you gain by voting Democrat?
Economically: middle class tax cuts, improved health care coverage, more funding for education, etc., etc.
Socially: a better environment, improvements in medicine (embryonic stem cell research), protection of constitutional rights, decriminalization of marijuana, more social equality (white/black/gay/straight/man/woman/etc.), upgrades in green technology, more freedom in general, etc., etc.
Politically: the separation of church and state, the implementation of progressive ideologies, a President who doesn't embarrass the entire country and butcher simple words like "nuclear," etc., etc.