Any attempt to block access can be bypassed just as easily or easier than applying the block in the first place. All the person needs is VPN access to a location that you don’t have blocked so that all their traffic appears to come from there.
The measures you suggest will prevent you wasting bandwidth on people who have accidentally selected your site when they are really looking for one located elsewhere but it will not stop someone who deliberately wants access to your site…Chances are that a small percentage of the visitors your stats say are located in the US are actually located elsewhere.