I did the 200 to 180 swap last summer. I went from an Avon Cobra to a Dunlop Elite (I think). Anyway, made a noticeable difference in the way the bike handles (sorry, I've got a 2014 Cali1400 Custom). Also sped up the indicated speed a whopping 10 mph at an indicated 80mph (GPS said 70-71). It also sped up steering input quite a bit. Almost to the point of feeling "twitchy" up above 80mph (real). For a touring bike, particularly with two up, it very well might be an improvement. But with my generally non-touring, single rider mode, I'm not real sure I like it, as the bike handles very responsively already for a 700lb behemoth. I may very well go back to the 200 on the next tire change, just to make sure it's an improvement to me. The smaller tire DID make a good 15 minute improvement in mounting time, and I didn't have to do anything funny with moving the brake caliper/rear shock out of the way. Like I had to do to get the big Avon off the bike.
Your mileage may vary... ;-)