Mechanics, belts, etc. aside I can tell you that moving from a 750 lb relatively old tech ST1100 to a 500 - 550 lb modern 800 or 900 cc bike is a bit of a revelation in terms of lightness, maneuverability, handling and just enjoying the ride.
There is a downside in terms of no shaft drive, there is less weather protection and, really, nothing compares to an ST or an FJR type bike with an RDL for all day long distance riding.
Also, IMHO, if you are going to be doing a lot of 2 up riding you should really stick to an ST, FJR, RT or some type of large sport touring bike. Not a consideration for me, so the Tracer works very well for me and I have no regrets.