I'm not sure I see how any of those things are problems, particularly since it's just syntactic sugar for things you can already do and would still be even if I were suggesting that assignments become expressions (which I'm not), though I could point out that of other languages in the same family, Python has operate-and-assign as statements (but not expressions), and ECMAScript has them as expressions, and I don't think either has suffered from having them.
I think whatever problems those may be are less severe than any of the current alternatives to writing code like:
.... which, given the current operators, requires either defining extra locals for what should be very simple operation, or putting a lengthy _expression_ on both sides of the assignment.