That's an issue that I'm struggling with now. My new-to-me NT will be replacing an ST1300 so there will be a drastic drop in available power. It has caused me to think quite a bit about how I use a motorcycle and the different kinds of demands I make of them.
By far the most use I get from the ST is long-distance travel with a full load of camping gear. There are times when I want to punch it and leave my partner behind on his PC800, usually when we come upon some curves after many miles of stupefyingly boring straights. While the desire to 'punch it' on the road has waned a lot over the last ten years, the need to lean hard has not and from what I know about the NT, I'm sure it'll perform up to my own abilities in that area when the chance comes along.
A few years ago, I spent a lot more time on the local twisty roads, the ones where the LEOs rarely go and few motorcyclists have yet discovered. We are blessed to have a good supply of those in this part of the world. I've done a lot less of that kind of riding lately and I hadn't though about why until recently. The ST, while very good at that kind of riding, isn't really made for it. It's huge and heavy and it's power is the only thing that makes sporty riding possible. So I think that a some point, I'll look into getting a small sport bike. I'm thinking about something like the Honda CBR250R or maybe a 250 Ninja. I don't mind shifting a lot, in fact it adds to the experience. One of those small bikes, properly fitted, would be more fun than forcing the ST to act like one of them. And they don't cost much either, so I wouldn't feel too bad about thrashing it around some.
Of course there's also the pack mule/urban chore/off road bike category and for that I have a Kawasaki Super Sherpa. That bike will probably continue to get the most seat time just because it's effortless and it's fun and I can get a whole lot of stuff packed on it.
I think that separating my sport and my touring between two more specialized bikes will be very good for me. I have no need to tear up the roads when I'm hundreds of miles from home with a lot farther to go, and there's no reason to push a 700 pound bike through curves like crazy if there's another option. And when all is said and done, I really don't think that a liter plus is absolutely necessary to get any of those jobs done.