Somewhat inspired by the Foodwriting post in the general forums... what if we had street festivals? Somewhat like a semi-regulated EOTW party, it could help extend the party idea past beta! I mean, who doesn't love a good party...?
On to the idea: I like Morticia's idea of a sandbox for art, but perhaps not with a permanent location and/or auto-clear. What about a combo of ideas, like getting a permit for a street fair/art show? Somewhat like an EOTW party in that it's informal and could be held anywhere, but also like an IRL block party in that it basically shuts off a street for that particular event. Go to the Bureaucrocs and pick up the permit, and it lasts for x number of minutes/hours/days from the time you get it. Maybe with a bit of lead time, to warn folks in the street that there's a festival coming and they should move their cars so they don't get a ticket... erm, I mean, remove any chickens so they can keep squeezin' 'em... erm, or something.
Like a RL art show, it's limited-time-only, and everyone involved is responsible for getting it all set up and torn down before it's a free-for-all on all the items used. Folks can still get through the street, of course, but the critters are all cleared out (maybe?) and everything's on lockdown except to the permit-holder and whomever they decide to designate as helpers (no limit on helpers, but helpers have to get permission from the permit-holder). In one street, for a designated period of time. Permit expires, that's it. Maybe with limits on how many shows could be held in a particular street and/or region in a certain span of time, so we don't end up with streets on annoying extended lockdown or anything.
Honestly, I'd be thoroughly entertained to stumble upon a random block party. Banners hanging! Strings of flags! Music boxes everywhere! You could even pay for an extra contract to get Helga to show up and sell drinks!