I'm not an archaeologist, but I play one on the DS.
Not resolving the money was the correct choice... it isn't required (George's financial problems are resolved without it in a way that's more supportive of the message) and extend the resolution longer than needed.
Modern films often make the mistake of having overly long resolutions. A modern version would probably feature an additional 5-10 minutes of "the next morning" with everyone saying "Hi" to George as he walks down the street, Potter being dragged off to jail, and a shot of Clarence flying around heaven talking to the angels. Essentially a lot of pointless things, when the best resolutions are short (look at North by Northwest... it goes from hanging off a cliff to the end screen in seconds, with nothing wasted). The worst part of all would be seeing Potter get his comeuppance as that would detract completely from the message of the film... it is not a film about the Baileys versus Potter, it's George Bailey versus himself.
It's also better to leave things open... with things continuing on, George never getting out of Bedford Falls, doing his best to better the community and prevent an $8000 stronger Potter from taking over everything, the only difference being that George now realizes how big his role is in the world even if he doesn't get to see everything and build all those hundred story high skyscrapers and mile long bridges. If Potter was given his comeuppance, that all sort of falls apart... the villain is gone and George has no opposition, a simple random act of Uncle Billy losing the money is all that was ever required to get a perfect happy ending where George is suddenly free to do all the things he wanted to do without ever having to care about Bedford Falls ever again. The message loses impact if the fight were to end... George would have his epiphany after everything was pretty much already done.