8 interchanges from 4 players is plenty. It's meant to be tough (it's not tiddlywinks). Whats next, different teams for attack and defence with breaks after 20 mins?

Agreed. The ability to play extended minutes effectively should be an advantage, but a high number of interchanges negates this somewhat.
We seem to agree that our concentration on speed around the ruck lowered our all round playing skills, less interchanges would push us toward playing with more brains rather than all brawn.

As for injuries, I'd say the fewer number of fresh forwards trotting onto the field would help reduce the number of injuries thorugh high impact.