The data says the opposite of pretty much everything you say here. The largest growing portion of the population is rural Latinos. They are particularly concentrated in all the Usual Suspect states: TX, LA, AL, MS, GA, FL, NC. (For some reason SC and TN missed out.) Just as Dems have "black belt" seats in the deep south and "brown belt" seats in TX, they are going to only get stronger in the rural districts those families settle in. Some first gens are intimidated by the local yokels but second gens aren't going to play that -- just like blacks became an important regional voting bloc in the south, Latinos are going to be VERY important in 20 years throughout most of the south.
The GOP also has a marginal return problem. Their base is far, far right, so when they produce a new generation there's nowhere for the distribution curve to go on the right side, so the median moves back towards the center. The Dems have virtually no hard left (met any actual communists lately?) so the normal distrib in their next generation still preserves the mean. The Dems had the same marginal problem in the 70s -- they were already pushed up against the window on their left, so their right wing fell into Reagan's hands.
All of this can be avoided if the Republicans have an internal realignment, but they won't: (1) until they get stung REALLY hard at the polls, the internal dynamics won't allow it, and (2) even then, the right has a problem the left did not -- a big part of its base is utterly immobile because it functionally equates voting with religious faith. Not only won't they move -- they won't allow the party to move either. We already see this "Fear of Apostasy" problem on immigration. Everybody in the GOP with an ounce of sense knows they have to cut the racist rhetoric. But everybody who got less than 90% in their last primary is terrified of somebody running to their right. So the short term profit for individuals is the long term devastation for the national party -- again, exactly what happened to the Dems in the 70s.
The final thing is this isn't your father's Democratic Party. Believe it or not (and I had a very hard time believing it), the Dems have actually got their act together for now. They over-performed in 2006, 08, and 12. They are going to perform at par in 14. (They did underperform in 2010, but I think they learned from it.) Eventually they'll fall apart again -- every heterogeneous coalition is unstable in the long term. But the GOP used to be able to sit back and wait for the Dem implosion. That just isn't happening anymore.
