You are asking the wrong question. The point of showing the number of items in the cart is to show the 'Status' of the cart. It works as a really good signifier to the user that he has added X number of items in the cart.
Scenarios to think when you do not show number of items:
You add an item to the cart, but, actually the click didn't register and you are unaware of this. There is no way of confirming the 'addition to cart' without manually click the cart and viewing it after every edit.
You double click an item and it gets added multiple times to your cart. Same as above, action cannot be checked unless cart is manually inspected.
These situations can be fixed by changing the interactions and designs during the add to cart and other related phases, but, why would you like to go through that much work when you can just show the number directly.
On a personal note, I would be quite frustrated and might end up never visiting the site again if it did not match such basic expectations. It's a terrible user experience.
On the matter of price, I think it matters to show the price in certain cases where you have other restrictions eg: Minimum bill of 20$ required for home delivery or something.
In such cases it helps the user keep track of how much he needs to order or not.