I very much doubt there is a "should be" approach to this: as others have pointed out, it really depends: on the company, sometimes on the industry too, stage of development, the team you're a part of, your personal work style, your manager's expectations and so on.

I've personally experienced both extremes, in companies that - at least from the outside - should be quite similar. One company expected that I work almost exclusively on unique initiatives, to the point of nearly neglecting my core work; the other valued and emphasized core tasks and welcomed what you refer to as "unique problem solving" only after the mundane was fully dealt with.

Needless to say, I didn't think that either one of these extremes was ideal. However, I believe that the extraordinary should remain, well, extraordinary. Most people can't function day after day, quarter after quarter, in a state of continuous awesomeness, one also needs time to decompress, recharge batteries, and fall back onto the familiar.

If I was to mention actual numbers, I'd probably feel that a 60 / 40 split would be ideal (60% core tasks, 40% unique problem solving).