Personally, I think that would be plenty for 3 days. It definitely depends on where you are eating and what souvenirs you plan to buy. I would try to predict/budget for food first.
For example (and these are averages/estimates, actual prices would vary on location and food choice, obviously):
2 CS meals ($15/person each meal) and 1 TS meal per day ($45/person each meal) + snacks ($15/person total) = $180 per day for food x 3 days in parks = $540 total
That would be more if you choose more than 1 TS meal per day and less if you choose 3 CS meals per day and even less if you bring your own food or snacks.
But that would leave you with just under $1000 for souvenirs, which is a LOT in my opinion, but, again, that could go fast depending on what you guys want to buy.
Others may have input that could help.