There's a difference between being a regular visitor and a frequent visitor. I'd call visiting once every two years being an occasional visitor, and I don't know that that merits special discounts similar to an AP or loyalty program. If the criteria for perqs were that wide, wouldn't everyone qualify for a discount?
I know I make a choice every year between being a frequent or occasional visitor. I can choose to visit multiple times and purchase an AP to get dining, merch, and hotel discounts all year. Or I can just buy hoppers, only visit once or twice, and not get any discounts.
I wonder, though, if you may be talking about people who only visit every couple of years, but those visits are long visits, as most DLR visits from your part of the world tend to be? If that's the case, you need to bear in mind your travel market has access to far longer ticket media (i.e. 10-day tickets, etc.) than we have access to domestically. So biennial visitors from Aus & NZ are already receiving a discount that we in the States can't access. If we want to visit for more than five days at a time, we have to either purchase additional, expensive single or multi-day tickets, or purchase APs.