From a practical perspective, I know that an additional $1.00 does not have a great deal of utility (or value) to me...personally.
I have plenty of $1.00's so one or two, or even one or two hundred, doesn't really mean all that much to me.
My brother, on the other hand, lives pretty much hand to mouth. He's unemployed much of the year and has a very difficult time making ends meet.
Maybe once a year, generally in the spring, I'll have him over the house to do some clean up. He does basic yard work type stuff (rake and bag last year's mulch, throw down some top soil, seed the lawn, throw down new mulch, etc...).
I called him this year and asked him if he was interested. Sure he says. Okay, I'll give you $200 for the day. Make it $300 he says. Done, I say. Just like that.
To me, $300 has no more value that $200. I'd pay $300 for a job I initially planned to pay $200 for without giving it any thought at all.
To my brother $300 has a great deal more value than $200.
Now, let's say that instead of asking for an additional $100 my brother asked for an additional $1000.
Could I afford it?
Yes. It wouldn't hurt me at all really.
Would I spend it on this?
No. I'd go out and do my own yardwork because the utility of what I am being asked to sacrifice excedes the utility of what I'm acquiring.
That right there, to me, argues indisputably against the notion that money doesn't have marginal utility.