What does it and the other two Democratic gains mean? There is nowhere on the map that a Democrat can't compete. Sure, the candidate has to be in tune with the local ethos - you won't run a Los Angeles Democrat in San Angelo, TX or vice-versa - but you don't do what Democrats did for decades: Not show up. 2004 was the last timid election for Democrats, and now the GOP has gone from 230 seats in 1994 to 199 seats and falling.
You're not going to always win these fights. Most of the time you will lose. But for the love of God, just show up.