You know you're too rich when your bank has the number 9999Q (Quadrillion) over your money.
You know you're too rich when 2 Million gp looks like nothing.
You know you're too rich when you can buy 200 marble blocks.
You know you're too rich when your house is 3 rooms on the ground floor - a hall, a parlour and a garden - and the hall contains a marble spiral going up to another hall with 3 rooms - 2 halls and an extra room - etc.