Hi Moffitt,
Firstly, excuse my alias - I set it up to use on another discussion group and stumpled across this thread whilst browsing!
I'm no financial expert (I trusted the Icelandics!) but I think you are spot on.
If you have always been able to pay your mortgage, then any saving due to reduced interest rates is effectively a tax free investment at your mortgage rate - not a bad return. Also, if you pay any saving off your mortgage now, you won't miss the money when interest rates go up again - simply reduce your payments (on a smaller capital). Also, if you have endowments, this will help mitigate their dismal performance over recent years and help you to reduce your shortfall.