It's a fair question, guv. No doubt about that. And one that I'd suggest all commentators (on any political subject) ought to ask themselves from time to time. Clearly, there's no guarantee that a more centrist, sensitive, nuanced conservatism would prevail even though I do think the GOP needs to rethink its approach as well as some of its policies.
However, you can also make a case for arguing that the GOP has not, despite being in the ascendancy, been quite as successful as is often imagined. True the party has held the White House for 20 of the past 28 years, but it's also the case that since 1988 the Republican nominee has only once (and even then narrowly) prevailed in the popular vote.
Perhaps, you might say, that's cherry-picking a stat and you might well be correct. Nonetheless, the only GOP victory (in the popular vote) in the last 20 years came in a) a quasi-khaki election and against b) a hapless doofus of a Democratic candidate. Beating John Kerry doesn't prove much. The United States may well be a centre-right nation in relation to other countries, but recently it hasn't been voting as a centre-right nation in American terms. And of course for most of the past half century, the Democrats have also controlled the House of Representatives. Sure, Bush scored a draw with Gore in 2000, but he did so by outperforming expectations and, absent Lewinsky and Gore's own foolishness*, would surely have been defeated.
Just as the purest liberalism is a minority taste, so too is whiter than white conservatism. And at the moment the longer-term demographic trends offer scant encouragement to a party that is increasingly perceived, not altogether inaccurately, as being white, male, elderly and religious. Of course, you need to look after your base but you also need to realise that the base is not enough. Unless it can improve its performance amongst "minority" voters then the GOP will need to do better and better amongst white voters even as those voters constitute an ever shrinking percentage of the electorate. In the long run that seems an unsustainable position. Yes, there may be some victories along the way but, as matters stand (they could change!), they're unlikely to be much more than exceptions to a general trend...
Obviously the GOP doesn't need to build a policy platform just to please me (that might also be electoral suicide!) but, again as matters stand, it's running against the grain not with it. That's a tough and dangerous spot for any political party.
*Another peril of punditry: assuming that the vanquished party was, and was always going to be, useless. Still, the list of defeated Democrats in recent years (Mondale, Dukakis, Gore, Kerry) is hardly impressive. In fact, the defeated Republicans (Bush Sr, Dole, McCain) is, I'd hazard, more impressive than the list of losing Democrats. This might suggest that Democrats can't win when they choose a poor candidate but that even a decent, more or less aceeptable Republican can't be guaranteed victory. Or it might suggest something else. Or nothing!