There is no "rule of thumb" but generally speaking, the more your credit is inflated way beyond your income, the more you could potentially have more "attention" placed on your account. Whether this will actually happen or not, who knows, but it's something to be aware of.
The bottom line is someone with a 50k income sitting at 500k in credit limits is going to appear somewhat risky to lenders because that's 500k in potential debt that the person will not be able to pay back for a very very long time. So you need to weigh your options. Don't accquire a bunch of credit you don't need. Just because some people here have 3, 5, or even 10 times their income in limits does not necessarily mean it's a prudent idea.
All credit decisions by lenders are made by assessing risk. You are shooting yourself in the foot if your limits far exceed your income. When your limits get so high with little to "back them up", you're treading into the danger zone, especially if you keep apping.
Now, worst case scenario, not the end of the world, one or two of your cards get shut down. But who wants to go through that? Like anything else in life, pick and choose your cards in moderation in line with your income and spend. Someone with a 50k income for example won't be able to spend enough to get real use out of 10-15 cards and 500k in limits. So reward wise, there's little point. You won't spend enough to reap big rewards from all of them. Keep things moderate. That's my opinion.
