My kids are still young ( DS 2.5 and and DD 7 months), and we are giving our kids one present from us and DS will get one present from Santa. For DS we are spending a total of $80 on both presents and DD we will be spending a maximum of $50.
My personal preference is that my kids are brought up to understand what Christmas is actually about and for us it is not about getting a heap of gifts.
But going back to the question about how many toys is too many.....if we were spending hundreds of dollars on their Christmas presents and then finances are tight for the rest of the year then they got too many toys.
Our kids will also be getting a heap of presents from aunts, uncles and grandparents .....and our house is already jam packed full of toys, so I think what we are giving them is sufficient.