When you simply need things to be flatter than flat, only one tool will do the job.
It's high time I got me some power sanding equipment, and there's really no replacement for a belt sander. Finish sanding is easy enough to do by hand, so I still view orbital and detail sanders as the tools of the lazy, but when you need to move a lot of wood quickly, getting some electrons to sweat for you is the way to go.
While I usually err on the side of "buy cheap, then replace with fancy when it breaks", I've already melted a few belt sanders in my day (oh, the painful memories of that peach fence) so I figured I should just cut to the chase on this one.
Of course, buying a $150 belt sander is a lot easier when you get the $50 refurb version...