I wouldn't extrapolate too much from state legislative specials. Congressional specials, definitely, but not too much (see: NY-20, NY-23, PA-12 in 2009/10).
Why would there be a difference though? Legislative elections have been shown to be obscure and far enough down ballot where opinions of the incumbent White House party generally dominate voters' decisions.
Personally I think we'll need to wait until after this November's elections to make more solid predictions, but these special elections have been showing some signs.
As for why is there a difference? Congress is far more partisan, and for the state level, there can be state-level waves that are independent of the national wave (see Kansas 2014, where Brownback nearly lost for example).
