i dont think thats really fair to be honest
sometimes you have to turn back because some **** snipes you, or in other cases when your attacking an op and the owner razes it so it will be a camp by the time you hit, its only fair that the resources are given back.
besides their ar eother ways to abuse the resource cap, haven't you ever gotten a boost while at max resources? it happens a lot to me on the owrlds i'm not playing or while i'm away and only able to log on for a few quick minutes.
you get max resources and then when the boost bar fills up you get 18k+ metal