When they are small is it much easier to keep it low key. But yes, when they get older it is much more difficult. When they start getting to 7, 8, 9 and up... then, at least for me, I fall into that "what I would have liked to have had at that age" and also the "what I'd like to see them use and would be a 'good experience' for them" type things. Bikes, scooters, cameras, good Lincoln Logs sets, Legos, painting, robotics, microscopes, telescopes, etc etc etc....
PLUS, all the stuff you will end up buying for them anyway, so might as well put it under the tree (clothes, shoes, favorite licensed team sports wear, gear to go along with their sport --for my kids that means new karate uniforms, and kicking targets--etc). And of course, beyond age 8, 9, you are talking serious stuff: ipods, or other handhelds, or gaming consoles, or electric scooters, weapons (martial arts, again).
I don't think we are on the extreme high end, but we will probably spend in the neighborhood of $400 on each of our kids. That seems to have been our running average over the past couple of years.
ETA: our kids are 10 and 13