it remains true that even a tiny and seemingly insignificant amount which people can easily toss around can still provide you a decent food.
Over 12% of Americans are living in poverty. It certainly isn't a tiny or insignificant amount to them.
Regardless of how you look at it, $4 is a significant increase from 50 cents. Given that that is a 700% increase, will you be saying the same thing when an average burger costs $32?
So, if the USD is losing 90% of its value since 1950, I would also assume that people's usual salary has also increase around 90% since then.
That's not how percentages work. Let's say a burger costs $1, and I have a monthly salary of $1,000 (to keep things simple). I can buy 1,000 burgers. If USD loses 90% of its value, then I can only buy 10% as much as I could before. My $1,000 will now buy 100 burgers at $10 each. For things to stay even, I don't need a wage increase of 90% (which would give me $1,900 and 190 burgers at $10 each), I need a wage increase of 900%, which would give me $10,000 and 1,000 burgers at $10 each).
Sure, wages have gone up, but prices have gone up more. In 1950, average household income was $3,000, and in 2010 it was $49,000. That's an increase of 16 times. Now, take a look at some of the costs of living.
Average house price - $7,000 in 1950, $273,000 in 2010. An increase of 39 times. Average car price - $1,500 to $35,000. An increase of 23 times. New York subway single ride - from $0.10 to 2.75. An increase of 27 times. The average family has significantly less purchasing power than they did a generation ago.
P.S.: Pardon me if I may be speaking out of touch of the US economic reality.
Although we are talking about the US here, the exact same situation is applicable to any western country.