Eyup,
There is a steady trade in Rockets in the UK, with used bikes generally holding their price well. The lowest price rocket in good condition is £6k for a well used 04-05 bike and that figure has been firm for years. That has had the effect of holding prices of newer bikes up to similar static levels. The release of the R3 has also seen a bump in values of post 2010 RIII's, with dealers asking nearly new prices for later Roadsters.
Sometimes bikes don't sell because they're either overpriced, or over modified. Standard bikes with Triumph accessories and tasteful modifications sell easiest, so buy a bike that's been well looked after.
A 2014 should be spotless, and with a full service history will suffer very little in depreciation in the current market.
Allowww.