It does get a little silty and the sand has built up in some areas also, the 4wd recommendation is reasonable. I moved to Canberra only a couple of years ago and Wingello is a good sandstone fix with a ridiculous range of climbing styles.
I have a 4wd but use it to putt down the tracks. I actually agree with the wet weather closures, people that intentionally drive tracks in the wet to test themselves ruin access for the majority of users. I would hate to see the area closed after such and investment. Some of the routes are gathering dust.