> This product should be operated in a well-ventilated environment and, if used inside a case, the case should not be covered

Does this make the B+ model more dangerous in case of overheating?

I have a couple of Pis running inside official Pi case they hold between 35 - 53 degrees. ( 35 meaning unheated room ). I would be sad if I upgrade the devices and then loose my sleep in case of overheating.