Well, there are definitely fewer conses in ((a b) 1 2) than in ((a 1) (b 2)), but ((a . 1) (b . 2)) has them both beat. (Maybe I'm missing something.)
As for being palatable to read and write, I actually disagree, even with the decrease in punctuation.
When writing a literal bucket, to add or remove a key-value pair, I'd have to edit in two places. Besides that, I'd encounter horizontal layout annoyances: I'd have to word-wrap the keys and the values in the same way in order to see the bindings clearly. And every time I added or removed a binding, I'd have to rewrap.
Reading is a bit more of a wash. When reading a bucket in debug output, it's harder to look up specific bindings but a lot easier to see what keys exist. I think I do those two things in about equal proportions (when I'm working on Penknife, at least).