I'm not prepared to submit to a dismissal of the Census Bureau numbers so easily. I would love to see a detailed analysis of them somewhere.
But, with respect to the points your raise, I'd say:
1. Generally it is mean (average) numbers that are considered to be misleading rather than median numbers. Mean numbers are skewed by individuals who receive extraordinary incomes. Median numbers just show the midpoint, the dollar income that half of individuals are above and half are below.
2. The points you make about what is included and excluded from the number is relevant, but its importance to the issue whether things are getting better or worse for younger Americans is not clear. First, I would assume that the items that are excluded from current figures were also excluded in 1973, so we still show a drop in real median incomes over time for those under 45 years old. In other words, we are measuring apples and apples. Second, I believe that I have also heard that the numbers do not include capital gains, which is an element of income that would be expected to be more significant in the income of older Americans.
