My homegrown plums were on the tart side and so the Creme Fraiche didn't really do anything for the flavor. I think if you're going for creaminess, make a custard. I made the same sorbet without the creme and liked it just fine.
I made this with home grown plums which are significantly sweeter than what I find in the grocery store, so I reduced the sugar to half a cup. It was delicious. Sweet and just a bit tart and just perfect on a summer evening.