Hot Spud,
Of the three Mayday calls I have heard over RT, all three were made on the local aerodrome frequency. Rather than spend money on a new radio, I would rather spend it on an ELT. That way you SAR people could home right to me instead of spending 45 minutes searching.
Having 121.5 set on a second box may well be a good idea for the cross country aviator, but I believe that the reason Crab has managed to get so many backs up is that he is perceived as expecting everyone to conform the RAF way of doing things. There is no resolution to this execpt to say by tuning into 121.5 increases your chances of hearing of TDAs and increases the chances of you being heard. But even if everyone did tune into 121.5, TDAs will still get busted and Maydays will still be missed.