@Arkandel
I think it really depends on what's happening in those public scenes. I'm going to be honest here and say I haven't read through the entire thread, so forgive me if I've missed anything or this has already been said. Specifically to answer your question:
I don't find incentivizing social scenes to be beneficial to finding roleplay. Your run of the mill coffee shop/bar/party RP isn't really particularly interesting and I see no reason to reward it with experience gain. Yeah, social scenes help you meet new characters, but is there any particular drive to seek out a character you talked about the weather and local sports with? Does it add anything other than a dimension of 'oh hey I recognize that guy' if you happen to run into them again? A +vote system, diminishing returns or not, isn't really an adequate substitute for RP creation.
Stuff that specifically drives a plotline (aspirations, if done correctly, or condition resolution, same) is what should be rewarded. Given the choice I'd probably want to reward conflict-driving aspirations with double beats or something along those lines. If 'start a bar brawl' or 'steal a wallet' is on your aspiration list and you fulfill it in some manner that creates in-game plot? You should definitely get extra beats for it. We're actually considering an +asp/conflict system for our game precisely for that purpose.
Incentivizing making stuff happen is what should be rewarded. This can be done from a player level or from an ST level. See above for player stuff.