I think the stadium thing should be situational. You should never be forced to play somewhere that isn't your local city. Namely places like Canberra, Newcastle, cowboys and Titans should all be allowed to play at their home ground for all finals.
Also I think stadiums like Aami park and WSS should be allowed for all finals matches. 30K is a more than adequate capacity for any final bar the GF.
This basically all came about because of pissing and moaning about big Sydney derbies being played in stadiums with too low of a capacity. If the local Sydney stadiums had the sort of capacity Melbourne, GC, Newcastle etc had this wouldn't be an issue. The furore starts because the media and the NRL don't want a match like tigers v dragons held at somewhere like Leichhardt.
Me personally I think week 1 should be any home ground. After that I'm pretty fine with grounds that hold 20K+ but would prefer 30K.
Having said all that within the next 10 years Sydney will have WSS, a brand new Allianz and a revamped ANZ. I don't think it's unfair to suggest most finals games should be played there.