Same here--we leave a permanent set in the slip. They are all tied at the proper length, so all we have to do is drop the loops over our cleats. But we carry a full second set in case we want to dock somewhere else, or need the lines for some other purpose.
Definitely the way to go.
I have two long and two short aboard the boat too, and they are different colours. So when getting ready to dock, when I use a long spring line around the athwartships cleat, we just grab a blue line from the locker. For a bow or stern line, black. Our other spare lines are white. Took a while to arrive at this arrangement but it works well.