Oh, that's a great strategy for tips!
Hosting parties for tip playing simply rocks the house hard. Like I said the guests that show up are an immediate captive audience. That's the whole key right there. If a guitar player just shows up in the park at any given hour, then a) there may or may not be any Sims in the immediate area to take notice, and b) if there are Sims in the immediate are when he starts playing for tips, they may already be engaged in another activity — picnic, conversations, chess, whatever.
Having a captive audience is just what making gobs of money from tips is all about. You can tell when an audience is captive because they're obviously looking at the guitar player. But, there seems to be a limit to a Sim's attention — and it varies from Sim to Sim. Some Sims can happily listen to a guitar players for hours on end. Others will only approach a couple times to throw money in the guitar case.
What I've learned to do is force an audience to be captive if I don't like the direction of what I'm seeing — too many conversations going on, too much dancing, etc. If those things are happening, then no one is approaching the guitar case. I stop the Playing for Tips and those audience actions immediate come to a halt. Then, I start up again and everyone becomes captive again for a while.
