I personally prefer two 4th Walls a year. Yes, it can seem too frequent, but you're not holding them every month. Six months is a long time in RPLand, with how quickly things can change and how fast people can come and go. No one's forced to participate; if they find they don't want to, they don't have to. I'll admit it's hard to do anything else during that weekend, but how is it any different than an event? Besides, it's only three days.

So, my vote is: keep them as they are. Two a year is pretty good.