Just ask the West Coast Eagle (up until late last year). they practice on a narrow wicket, when the got on the expanse of the MCG really struggled.Oh come on, I've never once heard "this match is so much harder because we are playing on a 6ft pitch".
A good spinner would love the additional width in a 9 foot pitch to entice shots from a batsmen, where a 6 foot pitch see that ball called no ball. Its also the width that the big boys play on.
Its not a big issue but the finals cricket should be played on pitches that most team play on week in week out.