Can one publish papers which give an improved presentation of old results? A colleague of mine (I'm in mathematics) has shown me a splendid note. He took some of the results from a confusing, hard to read, and important paper from the 1970's, which have not yet appeared in book form, and gave them much cleaner and simpler proofs, and explained them in a very clear way.

I urged him to publish his writeup, and to submit it to a very good journal. But he feels that, because the results are not (strictly speaking) new, the paper would be unlikely to be accepted.

Certainly I feel that work such as his is extremely valuable, and I think the mathematical community ought to encourage more of it. Was I right to encourage him to publish? Or was his pessimism more on target?
If the proofs are genuinely new, and genuinely simpler, then this is a contribution.  And if proper attribution is given and the relationship between the old and new work clearly explained, then this should be publishable, assuming that the results are still interesting for the wider community.