Throughout the Western world, this is what has been happening. The formerly right-wing parties have been marginalizing and then purging their most conservative members to concentrate on catering to "moderates". The result has been the same everywhere. The party loses support and also loses interest in fighting against Islamic Jihadists. If your plan of action is carried out, then in a decade the GOP will be down to about 150 House seats and 32 Senate seats, and both parties will be calling for cutting the defense budget to fund welfare programs, notwithstanding McCain's militarism.
The GOP has learned its lesson from 2006: the party cannot count on the votes of the fringe so we will have to forge a new coalition - the McCain coalition. Good luck wandering in the wilderness for the next ...oh, forever or so.
We might as well roam in the wilderness. Why remain in a party that will never again control either house of Congress?
BTW, any opinion on when the GOP will again control the California legislature, now that the state has filled up with your kind of people? How about never?