Yes season pass i think is better than 2 days ticket..
Price is similar but with season pass you got more.. I find quite useful Pizza menù (6,50€ pizza+nachos+0.5 lit beverage)
I know there are some vouchers for Gardaland winter opening and Gardaland sea life acquarium (~5min by foot from the park) but i don't know if there's something related to other merlin's
Both 62€ and 72€ season pass fastrack are referred to the whole season
62€ incudes 10 fastrack to use where/when you want over the season
72€ includes unlimited fastrack over the season but you have to choose between "Family Free" or "Adrenaline Free"
20-21 April.. It's monday and tuesday, i think you will find few people in the park...
I mean... this picture was taken last monday, march 30:
Imho 72€ season pass is good only if you consider visit again Gardaland this season (Magic Halloween Opening is awesome )
That's because those 2 days in april i think you probably won't even need to use your 10 fastracks included in 62€ season pass