Funnily enough, I was just thinking how interesting it could be for them to return, albeit in a MUCH darker form and with a non-comedic scenario. Moffat should do it just to prove a point!

I think I can see what they were going for with the Slitheen, though perhaps it's what I imagined from them before I actually saw them on screen.

I think underneath the fart gags and the lumbersome prosthetics there's a decent concept there. They're such a dark idea that both Doctor Who and The Sarah Jane Adventures gloss over the horrific side of their nature - here we have a species that skins humans and wears the remains. SJA introduced Slitheen children and showed their skins as well - skinning children alive and using their remains! It's actually rather twisted.

Aliens of London/World War Three was a very decent story though the alien design greatly let it down and I think they played it up for laughs a bit too much (can you imagine being on set filming it not knowing how successful or unsuccessful it was going to be?! It was the first story they filmed for the revival!). Boom Town was a touching and moral story that took things in the right direction. SJA's Series 1 finale The Lost Boy made it even better and had the dark child-kidnapping storyline, and also made it so that the Slitheen no longer needed to be 'fat'. It gave them a slightly more sinister edge, even if the story eventually slanted its focus to Mr.Smith turning out evil. The Blathereen then appeared in Series 3's finale The Gift and was again a more decent story.

I think if the prosthetics were made a bit less cumbersome and they were played a bit more seriously the Slitheen or another family from the planet could be a brilliant addition to the villain roster. Then again, you could always just design a new villain altogether.