Yes Ian, I agree. Average car ownership is 18 months, not sure about bikes.
There are bikes that I wish I had kept (most of them in fact). Most of us will want our first bikes back and I have had too many bikes to store all of them. I am in the same dilemma really. The 2, 2 strokes are keepers. The SV is the one I am convincing myself I want to sell. '02 plate with 20k miles on the clock, owned by me for about 2 1/2 years. It looks fine, runs and starts great and is enough to ride. That said, there is always something that starts calling to me. I have been looking (only on fleabay at the moment) at XT660's, FZ1's, FZ6's and Ducati's. Studying Land Rover Defender's at the same time. I don't need one, I don't want to do off roading, they are just calling me. I don't need any of them but......................................
An upgrade is not always the best choice. Better buying more storage and then buying another bike and storing the older one.