That's it really, but a 10 man wraithguard unit with spirit seer with conceal, joined by a farseer with fortune and a wraithseer using the Fnp power on them should be a great sponge for firepower .
This is indeed the case, but this is obviously a very costly unit. I've had a lot of success with (proxied) wraithguard in the past. When they're in their element, fortuned, concealed wraith guard are practically impossible to bring down. The problem is that, when your opponent does
bring something to counter them with (power fists, low ap weapons, etc.), they tend to drop far too easily for something as pricey as themselves. Termagants with poison can tarpit these guys for a while and do some pretty significant damage.
But yeah, spirit seers are nifty for any army using lots of wraith units. If you're like me and like to occasionally try a hybrid army using a couple of wraith lords, it's also a handy way to keep your wraith lords from falling out of spirit sight range, so if you've got a squad of warlocks or guardians somewhere, you might as well toss it on if you've got the points. Also, if you're like me, all your warlocks have it anyway because the codex entry for warlocks lists them as already having the spiritseer special rule. >.> Which I'm sure isn't a typo, and our opponents definitely won't expect us to pay the points to upgrade them to have the rule anyway.