My 1990 Kuwa Caravan has Ishiwata "EXO" quad butted tubes, not sure of the fork. It cost about $600 I think, expensive for me at the time, and I can see how yours was not that common. The Cascade looks like an interesting bike, I wonder how the frame design is diff from my bike, from how you describe it, it perhaps is beefier, who knows. I put this photo up on another thread when someone mentioned their Kuwahara, I don't think you were in on that, I could be wrong.

It came with 50/40/28 (Biopace) which I changed soon to round 50/40/24. I too find the middle 40 is a good setup with its good working range, although I prefer that to a half-step personally. The "velcro" MEC bags work alright, but when you put on the second bag, its finicky to get your hands through the spokes to do the velcro when the other bag is in the way.

As for affordable parts, this really touches on the whole cost vs "useability" ratio, when I look at costs of 10 speed vs 9 speed vs 8 speed stuff, it seems to me that it halves on the way down, and especially with the 9 to 8 prices, setting up a bike for someone like the 15 yr old son of the OP, it just makes sense to spend a quarter or less on parts that will pretty much give the same useability factor. Don't get me wrong, I have a gas riding my 9 speed brifter cross bike, but with touring gearing in mind, the diff between the 9 speed and my late 90s 8 speed Rockhopper is pretty much nothing.

I have often thought of redoing my Caravan, new bars, going bar end shifters, going 8 speed. I guess in the end, I would have to figure if it was worth it, as I could probably find a good, used, similar newer touring bike with little use for the same amount of all the parts changes....