When I hear of people trying to convince me that by witholding support they are sending a 'message' I think of PETA trying convince people to not drink milk. Noone cares that PETA does not like milk, but what gets people most interested in their cause is they use outrageous stunts to draw attention to their claims which have a pretty poor success rate in advancing their agenda.
Conservatives don't do enough to get the attention of the Republican party. If you become a wall flower the RNC will continue to ignore you. And if you think you are being ignrored now, wait till your non-support gives the office back to a Democrat. If the RNC feels the conservative base won't come home, they will seek out moderate votes to counter the supposed missing conservative base. Conservatives won't get their items they want passed by staying home. They will eventually get them by supporting the Republican Candidate.
No, what we get is people like McCain & Jeffords. If the conservative "base" is guaranteed by people who will mindlessly vote for anyone with an 'R' by his name, why shouldn't the party go as hard left as they can to pick up the moderates?