Seth MacFarlane admitted that American Dad was originally made as a way to vent his frustrations with the Bush administration, but it's clear Haley was also made so things wouldn't be too one sided. Stan would do stereotypically "Republican" things like discriminate against gay people, while Haley is a pot smoking hippie who barely does much to try and better her own life (and can be something of a hypocrite, like one episode opens with her decrying capitalism while at a mall, only to pull out an expensive phone and say "if you need me, text me on my Sidekick" [this was before iPhones and Android]).

Things have changed over time though since Bush left office around the time of season 3 or 4. The show's not as political as it used to be, so nowadays much of the humor is from character relationships and clashing personalities, and some pieces of character development do stick (Stan doesn't discriminate against gay people anymore, one episode even had him trying to help one of his gay neighbors be accepted by his homophobic father).

Pretty much. I heard it's because he wanted Family Guy to end around season 6 but Fox is forcing him to keep it going due to ratings, so he and the writing staff kinda stopped caring (I will say that with Cleveland back on FG it seems to be better now than it was for the past couple of years, but still not quite like seasons 1-6).

With American Dad it seems he probably likes working on that show more, so much so that when FOX tried ending it he had TBS buy the rights so the show can continue on a new network (one that seems to give him a bit more freedom too as the most recent season got away with a bit more use of stronger unbleeped swearing, something FOX wouldn't allow).