We usually go for 5 nights, and not including spending money on food - which we don't set a limit on - we usually spend an extra $400 or $450.
My 2 DDs are each given around $30 per TRIP to buy a souvenir = $60
I buy each DD a sweatshirt = $80
I get a few pins for me = $25
DH always forgets something like pajamas or bathing suit = $40
We usually do one special event per trip, like
MNSSHP or a tour = $150
A few activities at the Boardwalk = $40
DH suprising the DDs with some souvenir that glows in the dark = $25
Like many others who have posted, I have found that kids are much more careful about spending when a) it's their money, and b) it's a limited amount.
While I love WDW I really don't care for merchandise that has characters all over it, so there isn't much I'm interested in buying. If I lived in North Dakota and wasn't near good shopping I probably would have a different opinion on that.
Rest easy, you are taking more than enough money!
Nicole