Problem
a = a + 1 is verbose compared to
a += 1
It's a nice convenience that stops short of increment/decrement operators or keywords, which I suppose would be too C-like (the irony of Basic programmers trying to avoid C cooties when it's usually the inverse!) Plus, extending it to multiplication and division, while a further optional thing, is both consistent and equally useful, and goes beyond increment / decrement. Noobs don't have to use these operators. Call them "advanced operators" if you want.
I could swear that VB.NET and/or Xojo had this but I checked and apparently not. Maybe I'm thinking of FoxPro. Maybe I'm old and I'm hallucinating. I think it'd give you a leg up on the competition at any rate.
If it's nontrivial to add to the grammar then I understand, just thought I'd ask.