My hunch is that a lot of users simply accept all the defaults and never even go into their Profile to see the alternatives. Also at present, you can't see Userpics in 'top' view.
I do like your idea of a lean look but not by putting the 'message header' at the bottom. By its very nature it should be at the top. But we could put the Userpic in there and the message pane would be wider so we'd have more room for the extra buttons. There would be no wasted space at all and nothing omitted to achieve it. It would also make it easier for people to frame their forum with their own stuff down the side.
Seen in this light, 'side' view has nothing to recommend it at all.
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