Tough call, based on your stated criteria and preferences. I don't think you could go wrong, but I don't have the direct experience for a comparison. I have a Susie and a bunch of other Rivs, but my All Rounder is the closest analog to the Appaloosa. (If you cosider Appaloosa evolved from the Atlatis, which evolved from the All Rounder.... but it's pretty far removed at this point.)
I'll say that both are among the few bikes I'll never ever part with. But ESPECIALLY the AR, because it is just so classic looking and also so versatile. I suspect the Appaloosa will still feel more like a sprightly road bike than the Susie, with it's new thicker tubing - not the more "over-built" load carrier you're anticipating
On the other hand, I'll note that my one, big complaint about the Susie - a too-high-for-my-liking bottom bracket - is being remedied in the new, lugged batch. So that's a huge improvement that should make it feel more like a Rivendell and be more comfortable for the riding you describe.
I'll also say that you're probably correct that you won't want or need all of the tire clearance that the susie has. I got B65 fenders to work with 2.8 tires, with mods. (More on that later.) But it's way too much. It's overkill and doesn't ride or steer well. (But the high BB compounds that, Im sure, by making the center of gravity too high.)
Then again, it's nice to finally have MORE room than you need or want for a change. I think 2.5ish tires are probably the sweet spot - at least at my weight and terrain and for the type of riding you describe. (What I have on my clem) And, unfortunately, the Appaloosa caps out at 2.25 (going from memory... so check that.)
Making your decision even more muddied, I'm sure...