Your thoughtful answers align with my suspicions. Thanks for the news I didn't want to hear, guys...
Hillsilly, I still own two, rack-mounted film slide projectors that I used to wow people back in the day with one image "dissolving" into the next. The quality of the projected images was stunning, as you say. But with digital, people have since grown accustomed to fancy transitions and too, demand a level of photo quality that's at least equal to what they're used to seeing on their various LCD screens. This is where digital projection falls to pieces, as Brand B pointed out.
I guess I was just hoping that I had missed something. That there was some secret sauce, in addition to insuring the presentation room is pitch black, to getting the projected images to maintain good color, sharpness, contrast, etc. But it sounds like a new body and/or lenses won't materially improve on what the projector destroys.
Regarding my choice of lenses, Tron, I've actually been quite happy with my 70-300 DO lens. I think it gets a bad rap, although it took me a while to figure out how to improve its results: don't ever use a UV filter; always attach the hood; use a tripod when possible; never shoot wide open. All 3 of these lenses are small and relatively lightweight with decent build quality. In fact, when I'm on my smaller bike, I leave the 10-22 at home and go with only the 15-85 and 70-300 to shave off even more weight/bulk.
Anyway, it's too late and not practical to start shooting slide film, again. I have thousands upon thousands of digital shots from all around the world that I need to sift through and prepare for my presentations, even as I continue to shoot more. As I do so, I'm often disappointed by my Rebel's rudimentary focus system (it's inability to lock on a subject fast enough before the moment passes) and an abundance of noise above ISO 400. If I could fix these two issues, and keep my kit just as small and light, I'd be a happy camper.