instead of having to re upload the same cover every week. This create tons of copies for no reason

If one cover is used for Italian Restaurant night for example, every week you reupload the same image over and over

Instead we should be able to pick it from the uploaded images

If you are aware the event is repeating, you can set the event up as a reoccurring weekly event and the cover photo you use in the original will be used on following week events. Example: http://community.invisionpower.com/calendar/event/288-test/

Although, I do see what you're saying if you are creating single events one at a time there is no way to re-use a cover photo.