As an example of the cost of change, in some schools the transition to school's being governed by boards of trustees isn't yet working - and that change was initiated in 1989!
Minor parties (I include the greens in this category) add colour to the electoral process. They raise points of view that otherwise wouldn't get an airing, but the thought of many of them in government terrifies me. The only minor parties I have been truly impressed with have been Jim Anderton (Post alliance) and the Maori Party. Anderton is retired and Maori party look like they are history. Only the extreme ideologist or discriminatory minor parties left really.
Personally I am predominantly a National voter, but I have had no significant objections to recent Labour governments.
I'd like to see few cycles of National or Labour governing alone. Starve the lunatic fringe of oxygen.