I think a decent 'balance' between daily special % *AND* touchdown ability, when aiming purely for a Lv7 PoH's will be to;
1. wait for the day/s when the upgrade item is the daily special (duh!)
2. aim for the 80 -> 65 football Blue coolers + the 85 ->100 -> 90 football Orange coolers, with your priority being to aim for Orange vs. Blue when given the chance.
You get 2 upgrades via the quest line itself, and 2 can be had easy'ish via touchdowns. (just avoid anything that gives less than 4 yards min)
If you save everything up and don't spend at all until the upgrade item is the daily, then hopefully, outside of insanely awful luck, you should be able to bag the required 2 remaining upgrades.
Obviously, any footballs you might have left over once/if you get the 2x daily special upgrades, can then be spent going for the best yardage coolers, thus making it easier to gain more touchdowns.
Note: this all theory from following the beta test of the event, AND, assuming 0 diamond usage is the goal!
Obviously things will get *really* gakked up if we get the upgrade item too early in the event... or if a player can't keep up with the quest line, wants other rewards + Lv7 PoH's, etc...