There's of course a setting to exclude some dirs from being listed in the Latest symlink. It's called $zs(excluded,dupe).
Read the faq, there's an article about possible problems with it (and the solution of course).
http://www.inicom.net/forum/showthread.php?t=15531
What do you mean with "slow" ? It takes ~1 second here without other announces in the queue and between 2 and 5 (usually) when there are.