Correct, it is an enormous amount...Under Everett, the "number of worlds" practically exists on a continuous spectrum, so basically an infinitude of worlds. But this doesn't violate parsimony in terms of building a model of reality. I don't have the greatest comprehension of the history of science, but I imagine the behavior of water and gas was not initially explained as being the collective behavior of moles (6.02x10^23) and moles of individual molecules. The parsimony of thermodynamics is measured by the simplicity of the underlying equations that describe their behavior, not the staggering number of atoms involved.

As for observation, I didn't suggest there was anything special about observing. In fact, this is part of what makes Everett among the most parsimonious interpretations: While some (not all) other interpretations are tasked with explaining the nature of observation (what counts as observation, how quickly does collapse propagate, etc), under Everett, there is no notion of observation at all. My point about consciousness is that, being conscious, we are forced to have a point of view which depends on where we exist in/on the wave function. I wasn't suggesting that consciousness has any actual effect whatsoever on the wavefunction.

I admit that the nature of probability is among the most difficult parts of Everett to wrestle with, though I'm not sure I understand why subsequent observations should follow a radically different pattern? It's still the same wavefunction with the same distributions as before...Schrodinger's equation is the same wherever you are on the wavefunction.