Hi there!
He certainly used the Fleischer era for the (50% Sky Captain) look of the movie.
Though he recycled much of Donner's Superman the Movie with regards the storyline.
So basically, Singer's "progressive" vision was to ape the look of the 40's, ape the story already told in the 70's and take the 'super' away from Superman by making him a complete pansy.
Rather than a strong central male character people can look up to, we get an insecure, morose, bungling, wimp we are meant to pity.
In a way its almost as if Singer reversed the character of Clark and Superman in the movie. Kent actually comes across as the far stronger personality (to me at least), and I also though Brandon's superb performance in the Kent role was infinitely better than his (very limp in my opinion) Superman.
To answer your original question, no, I don't think Singer was going for nostalgia.
I think what he was trying to do was target the adult female demographic in the misguided notion that the action/adventure audience and young kids demographics would just turn up 'simply' because it had Superman in it. However, I think he alienated those latter demographics far too much.
It was also monumental hubris from Singer to basically ignore the two biggest demographics for Superhero movies, in his pursuit of the third demographic.
However, his folly was ultimately exposed by the poor box office figures.
If he gets another bite at the cherry lets hope Singer both acknowledges and learns from his mistakes!