I fully agree regarding the congestion on 121.5 with chat, burps and calls to ops - the miscreants who continue to do this should be fined. Regarding "practice pans" my view is that it should be encouraged - and in any event those practising are likely to be with instructors who would intervene should a "real" pan or mayday suddenly appear.
Regarding the other matter of radio congestion, I think it is a problem that has been unnecessarily exaggerated - sure it gets a "bit busy" sometimes, but ATC generally prioritise and recognise when someone needs to be called if it looks like their turn may be overdue.
As for sailing through FIR's without noticing that nobody appears to be talking to you (because you screwed up or misheard a frequency change), then my suggestion is that you go and get re-trained. You can't have it both ways - you complain that the radios are too busy, but don't recognise your likely screw up when it's all gone quiet!!
Sooty