Interesting stuff, Giloc. The hugely relevant thing will be if one gets lower minima with the GPS approach than with the existing one.
Otherwise, there is no real point. Anybody can fly an NDB approach using the GPS and I think that's what most IFR people actually do; you check the ADF on the outbound/inbound (to eliminate gross errors) and the rest is flown on the GPS. Then you don't get the awful ADF errors which can be 30 degrees or more (especially at Shoreham) which, if you are to fly as per the book (maintain the ADF track) make you chase the inbound track around so much you are not in a position to make a safe landing when going visual.