Well, for starters, although Britain was in much better shape than the rest of Europe after the war, they had been subject to a massive aerial bombing campaign by the Germans that left much of the country's infrastructure destroyed. They were lucky enough to be across a body of water, which prevented a ground invasion, or things would have been much worse.
Second, the Marshall Plan's effect of helping Europe recover its economic and industrial capacity was ultimately instrumental to the American goal of preventing Western Europe from falling under the influence of the USSR, as William R. Keylor details in his Twentieth Century World and Beyond (pp.243-246). Britain was no exception to American policymakers' fear that Western Europe would fall under the Soviet sphere of influence, so the Americans offered massive assistance to every Western European country except for Spain in order to try to prevent potential pro-communist upheavals in that region.
Alliance. They shed a lot of blood with us.