We love the 1500 loop for a pop-up ... small and near the Meadows Recreation area.
We have gone in late March/early April many times and the weather is usually perfect.
Don't know about anything special being done at the campgrounds for this ... never noticed anything, but there many have been some activity ... none that we happened to notice though.
Just know that the weeks surrounding Easter are JAM-PACKED with people. Full campground/hotels, capacity crowd at the parks (to where they are closing them), long lines .... on the good side, longer park hours.
Book early!