In my opinion, it depends on the public holiday in question, and whether or not it comemmorates a specific date. If the public holiday in question does commemorate a specific date, it shouldn't be "Mondayised"; if it doesn't, it's a good candidate to be.
So, I'd keep New Years, Human Rights Day, Freedom Day, Youth Day, Day of the Vow, Christmas Day and Boxing Day as they are now, and good luck changing Easter Weekend, but Workers Day, Womens Day and National Braai Day can all be observed on the closest Monday to the actual date.
It's the same thing with NZ public holidays. New Year, Easter and Christmas are on their specific days, and the two days commemorating specific events (Waitangi Day and ANZAC Day) are always on the same dates, but the rest of them (Queen's Birthday, Labour Day and each region's regional holiday) are usually observed on the nearest Monday. (Some of the regional holidays are observed close to other public holidays, so those regions end up with extra-long weekends.)