They aren't meaningless. As of now, they are essentially even (DBM is cherry-picking the pro-GOP ones, obviously), but that's something in a nation that generally claims to be more Democrat than Republican. Part of this is, of course, the fact that most "independents" are actually Republicans. Independents are liars, by and large. Most of them lean one way or the other, and strongly. And a higher number of those liars are Republicans.These polls will mean something when nameless generic candidates are on the ballot.
But even so, the generic ballot trends are telling. I know the Dems are being given a 1-in-3 chance of keeping the House, but I'd be absolutely shocked if that happens. I think a GOP win in the House is a forgone conclusion.