The ST1300 was always intended to be a stop-gap motorcycle, a tool to do longer trips and carry more stuff. It is, without a doubt, the best an ST1300 can be and it will ride the wheels off any stock example. Over the last year, I've gotten a lot of feedback from my riding friends, people who are very accomplished instructors and racers; the consensus is that I have reached the limit of what the ST1300 can do (even with all the upgrades). It's a good motorcycle, but not a great one.
On our most recent trip, I passed a CBR1000 and a Ducati 1098 while fully loaded for a 4 day trip. The 1098 actually blew one corner hard enough that I nearly took him on the inside - I decided not to for safety reasons, I wasn't sure what he was going to do. Anyway, the point is that people who assess riders' ability are telling me that the bike is now the major limiting factor in my riding, that I would be more comfortable, have more fun, and have a greater margin of safety riding a more capable machine.
I'm also told that a good bike might be coming up for sale soon for a very reasonable price, if I can make that happen, I will jump on it and the ST1300 will be put up for sale. If I can buy this other bike in cash, I will try to hold on to the ST1300 until the first warm day of spring and list it then. It will be ride-ready and the tires should still be in good/ridable condition; bikes that are ready to ride in the spring are more likely to sell.
The KTM 1290 Super Duke GT is also a contender, and it makes more power than the Multistrada. Also, I don't think you need a 3" long 14mm spanner to get the spark plug out or a special socket to remove the rear tire.