"Proposition Infinity" wasn't one of the greats, but it was a damn sight better than the previous episode. The relationship changes were a bit rushed, but you could say the same about a number of past romances involving Bender or Amy (heck, even Amy/Kif began as a throwaway gag), or indeed most of the romantic plots in this show. And the treatment of the issue could've been funnier if it had been a little more subtle here and there, but there were some excellent gags, some of which were subtler than others. (I didn't get "pre-op Transformer" until just now.)
This is the kind of "topical" episode that works better than one like last week's. Even if the most direct references are to a current issue, the debate over gay marriage, the broader issues of tolerance and discrimination are timeless. And casting it in a futuristic context, i.e. organic prejudice against robotic life forms, works better than past
Futurama episodes that have shown 31st-century society to be at about a 1960s level when it came to gender equality in sports or the military.
On the other hand you apparently missed the 'interracial couple':
They look kinda like Edna Krabappel and Seymour Skinner dressed up for a Trek convention.
Oh, and judging from the folks in the background, it looks like
rings are back in fashion.
For whatever reason, I found the entire clownitis gag very, very funny.
Whereas I found it a pointless intrusion. Too randomly bizarre. Something more sci-fi, like the brain slugs, would've worked better. And the brain slugs actually worked as a kind of subplot. This was just there for a few gags and then vanished.