I don't think announcing a new GBA is a bad idea. What happened to all the people on this forum who were saying DS and PSP were too expensive last year? A new SP will be $50-$150 cheaper than the DS and the PSP...that's a totally different market from the DS and the PSP. The top-loading NES and PSOne both came out near or after their successors, if I remember properly, so I don't think it would be a big surprise if Nintendo released a new GBA to try and spark some extra sales.
Also, if Nintendo really believes in the "third pillar" scenario, then keeping the Gameboy Advance alive must be part of its long-term plan. Now, I've always thought the third pillar plan is iffy, but that doesn't mean Nintendo won't go ahead with it.
As for Revolution, I've been convinced that Nintendo needs to show us something concrete this E3 and that's especially true if recent rumours about a mid-2006 release date are at all accurate. I don't mind if Nintendo wants to try and keep its "secret", but it's time to start generating some interest in the system. Give some info on the basic specs and bonus features (i.e. hard drive, movie playback, etc.) and find a way to demonstrate a game or two, hide the revolutionary stuff if you must. I'm prepared for Nintendo to just show a short reel of trailers, but hopefully that won't be the case.