Viability Wars

Does the leading candidate from one party impact voting in the other?
 
If Hillary looks likely to win the democratic nod, does that make McCain a stronger candidate for the Republicans?
 
Primaries are often an opportunity for "vanity candidates" to do well, and sometimes win (see GWBush), while more capable people are pushed away (see Biden, Bradley, Richardson, McCain in 2000). Especially when the opposing party is an incumbent or nearly (VP), it seems that parties do not send their "A material" to the slaughter (see Dole, GWBush, Mondale, Bill Clinton). And while sometimes the second tier candidates win against the incumbent/near incumbent (GWBush, Bill Clinton), parties seem to use that opportunity to air out their preferred positions rather than actually jockey for a win.  Vanity candidates like GWBush and Bill Clinton only won because of intervening factors, in both cases a strong third party that siphoned off votes from the incumbent/near incumbent.
 
But in an open election where both parties have a real chance of winning due to no incumbent running, I think voters may take viability more into account, and be concerned with the opposing party's likely nominee. If that person is someone that is wholly unacceptable (see Hillary, Huckabee), I think many voters will look at their candidates differently, and try and pick the one who is best positioned to win rather than the one closest to their own position.
 
In other words, if I were selecting a democrat to run against Romney or Huckabee, I would select the one who is the best bet to win (Hillary, in my opinion), whereas as a Republican selecting a candidate to run against Hillary, I would select McCain. McCain does not engender the hatred on the left that Hillary does on the right, so his success should provide room for vanity candidates (Edwards, Obama) more room in the next round.
 
In a general election, I think Hillary has the best bet to siphon off female voters from republicans, and McCain has the best bet to siphon off independent voters from the democrats. McCain also has the best bet to get hispanic support. That is the race that would be closest. I think Hillary would easily beat the rest of the Republicans, and McCain would easily beat the rest of the Democrats.
 
Interestingly, neither is the favorite of the party base, Hillary is too conservative for Dems, and McCain is too liberal (or at least random) for Republicans. But I think there is a good chance that Hillary will drive voters in the primaries to McCain's camp because as much as conservatives don't like McCain, they hate Hillary. But McCain's success will not be similarly beneficial to Hillary, leaving room for Obama to come back and be the Democratic nominee against McCain.
 
So in the primary viability war, I think it is advantage republicans, and the general contest will be McCain v. Obama...