When I think about it many Zoidberg centric episodes would work better as short(er) stories...
A Taste of Freedom is fine but it does suffer from containing lots of filler and is sort of anticlimactic. Lobstertainment I've mentioned above while Crustation in Love is also Ok but the story is just so cliched it would make a good subplot...
the things i like about the 'filler episodes', as you say, is that they spend more time showing the culture. the reason i love all of the zoidberg-centric episodes is because we get to learn about a unique alien culture. being a sci-fi fan, i especially enjoy these episodes.
The Decapodian National Anthem, FTW!