But both Man Utd and Chelsea change it up regularly in the Prem too, maybe not as much, but they do change tactics and personell. At the very least, their basic approach to a home game is different to an away game.
Fair dos on Barca though - I don't watch them enough to know if they do/don't vary it up (though I suspect you are right) so I see what you mean. I would agree that Rafa changes his approach more than anyone else, but then I don't think you can really judge how successful that would be unless we had a squad as good as Utd/Chelsea's. Personally I honestly think that if we had a comparably deep and expensive squad with a big enough wage bill to keep top, top players happy spending significant time on the bench you'd really see the value of Rafa's approach - I think he could do a lot better than either of the top two with their resources, but of course it's a moot and untestable point.
Two things I don't like though:
1) The idea that we can beat our rivals by effectively employing their methods with less cash, lower wage bill and a weaker squad and...
2) The idea that we can 'stop worrying about the opposition' while at the same time keeping Rafa's tactical nous against the 'big teams' - we wouldn't be as effective using different tactics against bigger teams if we didn't also employ them in the league every now and then, much the same way that Spurs and Villa fall apart when they meet teams that put 10 behind the ball and look to gain a point - Spurs especially will have an interesting challenge next season, because they're going to find that their direct, pacy, wide and countering style is suddenly going to be employed against a lot of teams that will hardly bother to attack them.
I know you didn't directly say those things - it's just I honestly think they kind of go together. If you want Rafa to stop 'worrying about the opposition' then you might as well ask for a different manager, and I also think you'd be nullifying our biggest strength.
That said, I see your point - the more successful managers in England have perhaps tended to have a defined style that they've stuck to more often than not, but I think perhaps teams have been effective due to more money and better players rather than that being, tactically, the best approach.
EDIT - this is probably a debate best had elsewhere though, you should totally reply, but I probably won't answer again (at least not at any length) because it's obviously getting way off topic.