I think it's bad any time people get used to something on such a habitual basis that they have trouble seeing new things objectively with an open mind.
Novel writers often talk about this problem. They read someone else's work, they love it so much they read it again and again, and it gets in their head so much that it harms their own ability to write a novel uniquely their own.
If you cannot even approach a new game system (and I do not necessarily mean 4e, since the OP isn't specifically talking about 4e) without thinking about it in terms of 3e, then you probably need a break from 3e. A a games creator, you've got to regain your perspective. I am not saying you need to quit 3e, just that you probably need a break.