The satin paper will last for several years so just put it aside somewhere dry, and preferably cool, until you want to use it later. I prefer the satin to the pearl MGIV but that's just me...

When wet the pearl or satin will essentially be glossy from the water on it so when they dry you will see the loss in sparkle that you describe. It just needs adjusting when you print - generally by printing at a higher contrast. A hair-drier can be used to speed up drying small RC test prints - I tend to just squeegee them as that alone gets them 90% dry.

Have fun, Bob.