I've verified, the Community Center event doesn't trigger until you enter the area on the next sunny day *after* the last bundle is done. Even if you were ok with leaving the desert, desert trader, and skull cavern inaccessible, you'd sell all your stuff (to whom?), turn in the vault with the profits, and then go to sleep, and as you headed out the door to trigger the community center cutscene, he would ambush you. So it's not a viable strategy, he's effectively unskippable as far as I can tell.
As far as Willy, it's not about the costs, it's about the time. If you're relying on it for 24+ different items, it could be *year 11* before one of them shows up. That's assuming you get a seed where they all show up at all, which is not guaranteed. I'm perfectly fine with completing this run by leaning on Willy and someone one upping it by skipping him as well XD