I do think that there is something to the way in which our view is shaped by innovation - the world of cinema is mostly driven by visuals (though I'm one of the biggest writing and sound geeks out there) and we tend to judge what comes afterward against our original impressions of stuff. So far, we've only seen Thanos at the end of Avengers, and this brief glimpse was a "huh?" moment for non-comic book fans. I think that it's smart for the MCU to provide more screen time and character to Thanos for Guardians, if only to establish the "this is the original big cosmic bad guy" character in the minds of all of the non-comic movie goers. This way, when Apocalypse and Darkseid come along - the average movie goer thinks, "Hey, this guy is kinda like the guy in Guardians of the Galaxy" and not the other way around when we finally get to Avengers 3.
The Guardians film is a landmark moment for Marvel Cinema in many ways - maybe most importantly from a story-writing perspective in that it blows the doors to the story settings/locations WIDE OPEN. If "Guardians" works, and if the general public buys into the idea that Star Lord exists in the SAME world as the Avengers, then you can send the Avengers off to ANY planet, ANY solar system, ANY space setting you want. Thanos no longer needs to come to Earth, you see... and we can entertain the story possibility that the Infinity Gems could assemble anywhere, in any galaxy.
If Ant-Man and Dr. Strange work, then we add in the concept of even MORE possibilities - the Microverse, alternate dimensions, and mystical realms - adding countless palettes for the writers to use in setting the stories.
Man, I'm getting excited just writing this stuff...