I agree with AKAK on this one. I have far less than his experience, less than a year, but I constantly seek to improve myself.
I do not like the idea of one plane for each tour, too boring. However. the argument that you get to learn this aircraft's strengths and weaknesses very well is very valid. I feel at home in a number of fighters, most noticably the F4U-1 and FM-2 and to a lesser extent the P-51B. But here are planes with which I don't do as well in (the F4U series belonged to this category until I persisted with them). So I may choose to fly a N1K2 instead of an FM-2, Fw-190-D9 instead of P-51 etc. You'll notice that the extra few percent of confidence you miss flying otherwise quite comparible planes makes quite a lot of difference. Suddenly you feel less able, less confident. I am perfectly capable of jumping from a Hog into a 109 (a greater contrast is hard to find) without disaster, but right on the edge, where it matters, it can mean the difference between life or death. And of course, there are always planes that will be difficult to master because they are simply uncompetitive. Having said this, SA is the most important here, not pure flying ability. A real ace will trash me one on one in comparable planes, no doubt. But an ace at a tactical disadvantage (especially with regard to numbers) will lose to an avarage pilot 9 times out of ten. Still, maybe it's the hallmark of a REALLY good pilot that he never finds himself at a tactical disadvantage. As far back as WWI, pilots found out that the best way to survive is only to fight at your own terms, never on those of the enemy.