You're on the right track with thinking of it as countable or uncountable. Consider the following difference:
I love to eat pizza.
I love to eat pizzas.
The first specifies that enjoy eating an uncountable amount of pizza. In this case, it means a portion of a whole.
The second sentence implies that I enjoy consuming multiple pizzas (in one sitting). So in general, you use the plural form when talking about an amount that could be more than one.
Here's another example:
I own a red car.
I love blue cars, too.
I would love to own a blue car.
I would love to own blue cars.
In the first sentence, I am specifying that I own (at least) one red car, so I use the singular.
In the second, I'm talking about every blue car, so I use the plural.
In the third sentence, I want to own one blue car, so I use the singular.
In the last example, I want to own multiple blue cars, so I use the plural.