For Legoland, I really don't think so. It's kind of isolated, and to get there you drive down a long, winding road, nothing else around.
For SeaWorld, there is a state park down the road (but we're talking like a mile or so), and you'd be walking along a BUSY highway, not worth saving $12 in my opinion. A friend of mine has parked across the street at a fishing supply store, but that was just for an hour to come meet us for lunch - I'm sure you'd be towed if you parked there all day.