Visitor Center

The Visitor Center makes it a little more convenient for you to collect trading cards from your NPCs. It costs 90 diamonds, which is not at all worth it, but you can trade for it without too much hassle. It looks like this:

And if there are cards to be collected you get a little icon over it:

And when you click it you see this:

If cards are available form any of those dudes, you'll be able to click the star and collect 'em.

If you have just a ton of NPCs I guess I can see how this would be useful. But if you find one NPC, you can click arrows to cycle through all of them and collect their cards, so that's really not very difficult. I do not recommend that you go out of your way to get the Visitor Center.

See, you click that arrow and just go through 'em all and collect.