Lately I've been trying different builds in WvW and one of them is PU power core mesmer with GS/Sword/X, and I must say that staff looks really tempting for the secondary weapon set. If we compare what each weapon can do we have:
and then we have Staff, with a nice low cd blink for kiting, 2 phantasms that apply vuln (and cleanse 2 condis with inspiration), chaos armor (that gives protection when traited) and chaos storm, one of the best stomp/ress denials in the game. Only problem is the lack of damage but for defense and utility it looks like a really good option.
Personally I'm going to try it next time I play WvW. Build would look something like this: http://gw2skills.net/editor/?vhAQJARWnsIClphNqBWoBcrhlTDxc3wZkBWU4sa0mA-jVSBQBEZ/hMq87BXAAA8AAwwRAYDHCg/q+jJVCiHdBkBQfMA-w
On an unrelated note, mass invis feels really good after the buff. Not only it helps you get some breathing room mid-fight, it also allows some pretty crazy stuff when you're in a group lol, be it random ambushes, ninja revives or just a safe escape from an angry zerg. I like it.