Inconclusive, I think. Ten years ago he was just running for governor: the number of things he had on his plate were fewer and the scope was smaller, as was his audience. The issues are larger, the audience larger, and the material decidedly more complex. I'd want to see something more comprehensive than these little spots, particularly since his malapropisms have been more or less constant since his presidency began.
It certainly doesn't prove anything, but even making allowances for the factors you cite, the difference in simple fluidity of speech is pretty amazing, no?
Yes, he was much more fluent. But in the clips from the gubernatorial debate, it's not clear that he's responding to Richards. As far as we can tell from this short video, he might be reciting prepared text. Not that I think he could recite so well today....but I feel as though the contrast has been exaggerated by selecting well-prepared thrusts from 1994 and weak parries from 2004.