Hi, Jeff, welcome to the site. Let me address your concerns as they're written:

Yep, the stock exhausts sound terrible. Or, should that be, *don't* sound terrible? This is easily remedied (see below)
There are no pros and cons compared to each other, it's purely cosmetic. The Speedie has twin disks up front and a tach. Seat, bars, wheels and a few other things are the minor differences and can be swapped easily.
Although I've not done vast mileages, I do spend a few hours in the saddle at a time with no issues. I've been riding for the last year with a slipped lumbar disc, too. Others on here have done the miles and, as far as I'm aware, haven't had any problems. Seats are easy enough to change if the stock one doesn't suit. The stock shocks/forks springs aren't great and are easy to upgrade; changing either of these will obviously increase the touring range of the bike. There are a few riders here who are, erm, of more portly dimensions; again, no complaints from them.
Your last little paragraph is a bit concerning. It's a Triumph, not a Harley, and if you want something that shakes and sounds like a Harley, perhaps you should buy..a Harley. This is a Triumph, you buy it because it's a Triumph and you appreciate what makes it a Triumph. It has a distinctive style, ride and sound of it's own. The engine is counter-balanced, although the Triumph engineers actually left a few vibrations in as a nod to bikes of the past. It is possible to remove the balancers but it's not a small job (I wouldn't imagine). Regarding the sound, it's never going to sound like a Hog, but why would you want it to? That's not to say you can't make it sound nice-loud, rumbly, deep, etc.-but nice in its own way. With the right pipes you can get the low tone that you're after.
My post isn't meant to put you off but, if you're after a bike to look, sound or feel like a Harley, this isn't it. As they say in France: "Vive la difference!!"

Audio clips

One of my favourite Youtube clips.

As for other things: it handles great, the engine's willing and reliable, it gets as much attention as you want, they're a doddle to ride, easy to maintain and have a decent aftermarket.

My advice to anyone would be to take a test-ride to get a feel for the bike and maybe try to find someone local with one to have a listen to non-stock pipes.

Ride safe, Neill