I think that monetary equality can be one good way to gauge overall equality, but it's not the only measure. Neither is quantity of gifts, or really anything else. It's important to take into account other factors (like how much the person wants a particular gift, what their interests are, how much effort it takes to give the gift, etc.).
I personally very much appreciate that my parents have always been aware of how much they are spending on one child, and do consciously try to keep things even with the others. But I have no idea if that translates into actual monetary equality. As others have said, it was the appearance of fairness more than anything else. Fair isn't always equal, but it's nice when the starting assumption is that fairness demands equality until proven otherwise.
I also think that how a gift is presented matters a lot. These weren't Christmas gifts, but there was one year when my brother, sister, and I all wanted to do things that were pretty large in scope, and not cheap. My family was going on a super awesome vacation, and my now-SIL (she and my brother were not yet married) was invited if my parents paid her way. My sister wanted to attend a multi-week program in another country. I wanted to move to another state to be with my now-husband.
So they paid for my SIL to go on the trip, paid for my sister to attend the program, and gave me seed money to move to the new state. I know how much money they gave me, but I haven't the foggiest idea how much the other two things cost. The reason why I think of them as equivalent in scope now is because my parents presented them that way. They told each of us what the other siblings were getting, and specifically said they had decided to pay for these three things because it was a way of being fair to each of us. It meant that none of us took away the idea that one or both of our siblings got "more" than we did, because my parents explicitly told us that we all got a Super Expensive Thing We Wanted.
I also think that when it comes to people who are different ages (like nieces and nephews), consistency is as important as equality. To give another example -- one of my uncles was very good about remembering birthdays. He'd send each of us a card and a little bit of money. He gave us the same amount of money as our age (so when I was 11, I got $11), sometimes with a bonus dollar or two for a milestone birthday. It meant that my brother always got more money than me, and I always got more than my sister, but it never felt unfair.
So if and when I have nieces and nephews that are far apart in age (which I probably will someday, as my older brother already has kids, and my younger sister isn't even dating anyone seriously), I won't have any problem spending different amounts of money on children who are very different ages, as long as I follow the same general trend for each one. So if I gradually increase the amount of money I spend on gifts as they age, I'd just make sure to gradually increase the amount of money I spent on younger children at the same pace as I did the older ones.
I think part of that will be based on interest, because the interests of a toddler are much more variable than the interests of a teenage. I'm spending about $10 on my niece and nephew for Christmas this year, because my niece is not yet two, and my nephew is a newborn. My nephew won't care, and my niece will be totally happy with the $10 gift I picked out for her. When $10 no longer packs the same punch, or when their interests become more long-lived (such that I'm willing to spend more money on the things they are interested in), I'll probably spend more.