Hairy,
My Clipper II is 3.5 years old and has 469.2 hrs.
I think I'll hang on to it at least 3-4 more years before changing it - everything works well and it seems a good 'un etc...
I say this having just had 2 months of downtime because of an engine problem in my equally well pampered Mooney which is newer and thankfully covered under warranty.
Knowing my luck when I decide to change machine we will be at $1=£1!!
I would change the clipper at 4-5 years but I have other commercial projects on the go at present (ones which will make me money rather than costing money as well as improving my quality of life) which require reinvestment of most of my current income. Anyway I have spent enough on aircraft for this decade.
All the best,
SB