I have 31k miles on my 06 K12S now. All but 1400 miles of that have been put on since Jan 07. I don't own a cage (have a K12S and an 02 K12LTC).
I never did like the GT, ie, looks, etc. For 2-up, there is none other than the LT IMHO (and the wife's opinion also, which is the REAL reason, heheh).
I have the hard bags but quit using them since I lane split every week, to the tune of 60 miles when the traffic gets real bad. I found the bags dont' give me enuff sqeeze space so I just put a helen's bag on the back seat most of the time now. The hard bags are nice when you need them.
Whatever you do, don't ride the S unless you plan on buying one!
I can't say enough about the bike. Its not a racing machine per say, a bit heavy on the turns, etc, however, it is the design of the bike that makes it good for long trips, etc, in comfort, if you like that sort of thing (comfort is relative).
I can't plant my arse on that seat enough, every day I walk out to get on the S its like a brand new pleasure all over again. I never get tired of riding or looking at it. There are not a whole lot of bikes out there that fit that bill, for me. I like the LTC and all too (93k miles on that one), but its just not the same.
by the way, there have been some killer deals on the K12S sister forum, that might be an alternative to a trade-in. If I did it again, I might go that route instead of new.