Six Flags memberships and friend pass cost

I've previously been a season pass holder @ SFNE, but that was years ago before they introduced the Flash system and the new tiered season passes. It was MUCH simpler back then.

I'm trying essentially to predict which pass(es) would be beneficial to buy now to result in the overall lowest cost for the summer. This is Six Flags New England, so it's not open year-round.

My oldest daughter will be going with school (can use a season pass) and we'll all likely be going sometime over the summer due to having guests visiting from Europe. So let's say she goes twice, plus 3 or 4 additional passes, plus parking once. They also have an adder for the water park, which I can't seem to find. So I am thinking of getting some sort of season pass for her, then using those benefits for the rest of the family to go later in the season. [I did something similar last season, it was cheaper to just buy her a season pass that included parking than a day ticket plus parking, WTF?]

Unfortunately for each pass type [sixflags.com] it just says "X specialty rate friends tickets" but what is that rate? The upcharge between Diamond and Platinum is $75 ($75 for Pt and $150 for Diamond) and besides a bunch of irrelevant differences like an additional 5% discount on food, gives 5 specialty rate tickets vs 2. Basically I'd need the price difference of the 3 passes to be around $25 vs. "standard" tickets (or at least close, then I can look at the other benefits of Diamond.

Wondering if anyone here has used these passes in the past and has an idea of the cost difference, and if anyone has an idea of when SF might be having discounts/offers on passes?