I disagree... I would probably wash it as is and put it into a vial for storage.
Just make sure you make a starter when you go to use it again... and confirm that it isn't infected and you are good to go IMO. That being said, I am really cheap and not willing to buy a fresh vial if I think there is a chance that I have some viable yeast... However, since starters (generally) don't contain hops, they don't have quite as long of a shelf life... so YMMV.
OTOH, why would you add dextrose to the starter? That is just getting the yeast used to eating simple sugars and making them too lazy to ferment maltose.