I tend to shop year round, and I think I do better with the budget that way than if I wait until November or December to look around for things for everybody.
That said, it's a fact that as children get bigger, the "material" pile gets smaller. That's the case even if you don't buy the megabucks game systems or the designer clothes.
I do like to spoil my grandchildren (I consider it part of my job description! I'm mentioning it because you may have grandchildren one day)... not that I don't stick to a budget, but I wrap everything separately so it *appears* to be more spoiling. The grans are still pretty young, but I know that system won't work much longer!
Keep in mind that, just as you have wonderful Christmas memories, your sons may have wonderful Christmas memories as well. They'll just be different from yours. What about asking them what their favorite memories of Christmas are so far? You may be surprised.