I don't have the answers to these, but I'm sure someone will after a while, and I'm very interested to hear them. By the way, this reminds me that I need to plug Brendan Nyhan's excellent column about what reporters could do better with election results, including the key point that reporters aren't well-situated to immediately offer causal explanations for relationships which scholars will tease out (and often fight over) for years. At any rate, here are the questions I'm wondering about in House elections 2012:
1. What effect to redistricting and gerrymanders actually play? This one is getting a lot of early emphasis from upset Democrats, but that doesn't mean that it actually mattered, or if so how much it mattered. (For what it's worth: my experience is that people are really fond of gerrymandering as an explanation for things, whether or not it's actually true). There's certainly some evidence, but nothing conclusive yet.
2. What effect, if any, did big outside money have? The emerging conventional wisdom is that most of the outside money on the presidential race was wasted (which many of us had anticipated), and that a lot of outside money on Senate races was wasted, too -- that one I'm not sure of, although certainly a lot of it went to losers. But what about House contests? That's where $1M or more coming in unopposed surely might have made a difference. Did it? If so, how much, and in how many districts?
(See, by the way, Matt Glassman's general comments about SuperPACs and wasted money).
3. What was the effect of candidate recruitment in this cycle? In particular: in Senate races, Democrats appear to have had a massive advantage in recruitment. Was that not true of House contests? If not, why not? I've been arguing that there's a systematic reason to expect GOP recruiting difficulties, and the Senate campaigns appeared to be evidence that the effect was real; what about the House?