The details in channel central are provided by the server and can be obtained without opening channel central. Keys are of course not shown if you're not an op. There is no reason why mIRC should not allow someone to open channel central when they can already obtain the information from the server in other ways.
As far as size, there have been multiple suggestions to increase that size or at least allow it to be resized by the user. Font size is probably not going to change, though that's just my opinion and Khaled may choose otherwise.