They pretty much have all things party covered. Music? Check. Drugs? Check. Booze? Check. Hookers? Check. Really, you need a party done, you call the Slaaneshi folks on over.
Y'know, since we're dealing with the Mechanicus and all, have a totally serious, legitimate, and Cult approved moral booster for those serving alongside Mechanicus forces.
See, the idea of boarding actions, zero g shenanigans, and the general coolness of space has now won me over. I'll vote for Space, though I am truly fine with either (And ground based operations on planets are fine and dandy too).