Change your sorting options if you'd like to see more recent entries instead. ;)

I have an advice here - ignore stupid / troll entries, don't up vote them, and they will simply dwell somewhere on the very bottom of the wishlist until they get deleted due to spam reports (yes, you can report spam and duplicates per each wish via Options menu).

Also, with the way the list is currently sorted and once it gets populated, low voted entries will remain stuck on the last pages unless you specifically look for the least voted stuff, so even if there is some spam for a period of time, it will not be that visible.

PS: last but not least - we want the wishlist to be clean (and therefore usable), so people purposely spamming it will be blocked from adding wishes / comments there.

At this point there isn't such thing as down voting wishlist items. It's not a bad idea per se, as long as it's implemented properly (as a separate stat for example), but we wanted to start in a simple & clean way and see how the wishlist evolves and what will be your suggestions. .
For the time being I recommend to express any kind constructive criticism regarding a wish via it's comments :)