They did show the slums, briefly. And one of the points is that without George, there would have been no affordable housing tracts- that was instead a graveyard. Remember how happy people were moving out of one of Potters shacks that they had to pay high rents for and into their own home?
Not to mention, Mr Gower turned into a ex-con drunk, Harry dead and thus the transports Harry saved was sunk, killing quite a few American soldiers. Not to mention, Violet would be a drug addled hooker. Jazz is all well and good, but drugs, alcoholism, homelessness, graft and corruption just means folks have to turn to ways of relief from unending despair.
No, see Potter got his just reward. The best revenge is living well. Potter lived the rest of his miserable life as a sad sour old cripple, who nobody liked. Another few thousand bucks aint gonna make him any more rich or happy.
Clarence didnt make many miracles, and revenge on Potter would be out of place. Clarence just showed George that his life really was wonderful, and Potters life was terrible.