I'm enjoying not spending a lot of money, I didn't really spend a lot with my other two either though. I didn't buy anything too expensive. Their cribs and carseats were under $200 each. My mom is obsessed with buying the kids clothes. So I didn't have to buy much, except when I found something I liked.
I saved all the clothes from my 2 DS and though I'm having 2 girls this time, they'll use hand-me-downs until they get their own opinions and want to pick out their own clothes. Though my mother insists that they need pink clothes. Half the stuff she gets for the kids end up never being worn by them though.
My big investment this time around will be cloth diapers. I'll probably have 4 in diapers when they arrive. My 3 year old hasn't decided that he wants to us the potty full time yet. He'll use it if I tell him to, but he's not ready to use it of his own accord.
They boys are still using their cribs as toddler beds and I have two pack n plays, which the twins will use for a while. Maybe by next Christmas I'll by twin beds for the boys and transition everyone around.
Other than that, I just need to buy a 5 point harness booster for my 3 year old and I'll have enough carseats. One twin will be in an infant seat so I'll have to still buy convertible (or another 5 point harness for my now 2 year old who will be 3 by then), which will be cheaper.