I don't think the Lemon test is necessary to rule the teaching of ID unconstitutional. All the plaintiff's have to do is established that ID is a sectarian religious belief with no scientific basis, and it would fail even under the most narrow reading of the establishment clause. Any unbiased reading of the trial evidence shows that they've succeeded in doing that.
Oddly enough, I'm with the creationists in hoping the Lemon test gets scrapped.
If you undo the Lemon test, you're still stuck with the cases that Lemon attempted to summarize in that three-pronged test. It's difficult to see how a state action that has no secular purpose could survive a First Amendment attack. That's prong one. Prong two says that the principal or primary effect of the state action must be one that neither advances nor inhibits religion. Will the Supreme Court strike that down?
I suppose that in some ways the Lemon test is too strict. If a state gives its employees a day off for Christmas, that would technically be a problem under Lemon, and it shouldn't be. I definitely see some wiggle room in the future. But not in this Dover case. ID has no secular purpose (except fund-raising, book sales, legal fees, etc.).
The plaintiffs' main argument is that the statement of the school board does not pass the Lemon test. Personally, I think it does.
The big question is whether or not the Lemon test survives. If it doesn't, the defendants will win. If it does survive, it's a closer call.