The two day, two park passes do not expire AND you have access to CityWalk. I think that these are good if you know you can only go one day/night, but you know you'll go back again for another quick visit. You save a little money over purchasing individual entries each day (plus, depending on inflation, you'll probably save a few $$ because you already have an admission ticket paid for for your next visit and the price will have probably gone up.)