I too am of slighter stature, also measuring 5' 7" in height.
I have owned my Rocket III Roadster for nearly a year, and have commuted through London traffic every day.
It handles beautifully and is lovely to drive in my opinion. I am however buying a cheap 350 to commute on.
You are right about the seat, it is a little wide and I am looking for a different option seat-wise. Because of its weight, you can't save it from a minor incident. One just has to accept you have to put it down.
The balls of my feet are both on the ground at stationary, but I can't help thinking a slightly lower and narrower seat would help.
My Triumph dealer said they could have it narrowed by someone they know, but I have also found Corbin do a seat which is narrower and slightly lower. Very expensive of course, but might very well make all the difference in the world, and be worth the expense.
It's a fantastic machine, Triumph are clever!
I own/ride a 2005 Rocket 3 Roadster, and have had it for about a year now and am also 5'7".
For a bike with a 2300cc engine, it is well balanced and quite easy to ride generally. A bit of a learning curve at first, but your confidence and skill get better every time you ride it.
I dropped mine twice (while stopped) with no damage to the bike or myself thankfully. Once my foot slipped on some mud while backing up, and another time while trying to pick up my glasses while stopped. For such a heavy bike, it's surprisingly easy to lift back up again though (well balanced).
You have to take the turns slowly as ground clearance is not quite as good as other bikes, but you get used to that.
Depends what you want in a bike, but I'd definitely recommend a Rocket 3 (a reliable ride with huge fun factor IMHO).