The Seaworld park has a Pay One Price ticket structure shows and rides are included. They also feature a good refillable mug program for soft drinks all day all over the park.
My family has been to Seaworld Orlando x4, DC X1, San Diego X2 and San Antonio X8. We tend towards two days at San Antonio but not a lot of competiion there like is with WDW in Orlando.
When in Combo with a WDW trip I would see Seaworld as a relatively easy park to tour except for the 4th of July Holiday crowd. I think you may have a pleasant time there but would expect the park to be packed as many will be coming out for the special night Shamu show they will have that night and the fireworks that will be done at closing so I wouldn't plan on light crowds or a emptying out that evening.
However I will venture to guess that WDW MK and EPCOT will be at least as crowded if not more crowded that day.