As a woman who married a spoiled only child, I beg you...please stop!!
I'm the middle child of three girls and we were taught how to earn the things we really wanted. That probably sounds fairly harsh, but it wasn't. My parents didn't have much money so they couldn't afford to buy us everything we wanted. At the risk of dating myself, when we were teens, we really wanted Nike's, but my parents couldn't see spending $30 or more on a pair of sneakers. Instead, they agreed to give us the money they would have spent on Trax for us and we had to earn the rest. We did get an allowance, so we learned to save the money for what we wanted.
My husband never learned to save anything. Do you have any idea how hard it is to teach a 36 year old man how to save? If you were to ask my MIL, she would tell you that she certainly did him a disservice by spoiling him. Just last week we had a discussion about our future and he pointed out that we don't have the money for the things we want to do (home and kids) then later that same day we were at the store and he's checking out the newest PS2 game that he wanted to buy...yet we've got a stack of games here that he hardly ever plays. He doesn't know how to save, budget or prioritize.
He's not a bad person and I'm sure your kids aren't either, but if you buy them the latest and greatest of everything as soon as it comes out, what are you teaching them?
I do like the other persons idea about donating the older systems because that will teach them to do for others. Another idea, take what you would spend on the new system...use half to buy games for their current system and put the other half into a college fund or savings account for them.
Hope you take this in the tone in which it was written. I don't want to tell you how to raise your kids, but I just wanted to give you some insight into what they could be facing 20 years from now.