I'm not sure whether your bubby is sleeping less because of the stimulation or due to her change in age. I'm sure for most babies they tend to sleep less and less as they grow older. Anyway, I never had this worry...
I think the REAL risk of overstimulation lies in letting your child watch TV (like cartoons) for long periods, unsupervised. (See our TV FAQs article in BrillBaby.com on this).
How old is your child again?
(btw, on this point, I would encourage you to fill out your baby info in your user profile page (under Account, Baby Info), so that other members can easily tell how many children you have and how old is the youngest one, as it is displayed under your name when you post).