Originally Posted by metaphysician
The thing is, those new characters would be completely irrelevant to the actual plot, 90% guaranteed. So you'd be cluttering up the story introducing plot elements that detract from giving attention to the actual focus of the story.
Anyway, there actually is an additional element of evidence against: the whole "he's adopted?" line in Avengers, which would make little sense if Thor himself were a bastard child. Nevermind the whole "at no point is Odin portrayed as a cheating bastard" problem.
He could have hooked up with Gaea, dumped her and found Frigga later lol. Therefore he still wouldn't be a cheating bastard