Zarhym has got some answers to the widespread problem of lag in Wintergrasp after patch 3.1 the other week. He says Blizzard figures the problem is simply population based -- there are many more people playing in the battleground than there were before the patch. For that reason, they're having trouble coming up with good solutions: the battleground is designed to be non-instanced, and that's why a lot of people like it, so putting a limit on the amount of people in there is not the way to go. Hardware isn't a solution either -- Blizzard's hardware is already top-of-the-line, and not only would upgrading it take a while anyway, but my guess is that most of the lag issues come not from Blizzard's side, but from the connections between players and them, which they may not have any control over anyway.
So yes, we're more or less out of luck -- as long as Wintergrasp is extremely popular (and even Zarhym remembers the naysayers before the release with a smirk), there will always be a certain amount of lag in there. There are a few good suggestions floating around the comments thread -- one is that Wintergrasp should always be conquerable, which seems like it would keep down on the flood of people, though of course there'd be other issues if that were implemented.
At this point, Wintergrasp lag may just be something we have to live with. Eventually, you have to think the population will drop back down, and then those of us still in there will enjoy lag-free battles again. But Blizzard has taken on quite a goal trying to do non-instanced PvP full of vehicles and towers without any lag at all.