It is purely for looks. (1) the smaller air filter element will get fouled faster and decrease performance; (2) running an exposed element air cleaner makes the carb suck in more hot underhood air which decreases performance and economy; (3) running an open element air filter is louder, especially in a van.
If you are itching to do something to your air cleaner, why not consider doing something that will actually offer both a performance and economy boost? Instead of running an open element air cleaner, try rigging up a cold air intake system. All you need is a dryer hose and some zip ties. Fasten one end of the dryer hose to the end of the snorkel on the stock air cleaner, then route it somewhere behind the grille and secure it so it won't be caught in any moving parts.
That's it! The cooler air will help your power and efficiency a bit, and is certainly more beneficial than an open element air cleaner.
I figured there wasn't performance gains, since its jetted to run with an enclosure, but wow, I love that idea! Makes total sense, it's super hot down there, and I really like this simple add-on idea and I will use it, thank you so much Reed!!!!