I'm sorry about your totaling your Dodge Magnum. :(
Funny that you have 3 car seats and a Toyota Sienna, since I do too. I love our Sienna, but I primarily drive our other car (I kept both cars when my husband left), which is a Toyota Matrix and which - and I never would have guessed this - also holds 3 car seats. I'm sure it gets great gas mileage because it's such a little car, although I don't know what it gets.
One of our car seats, though, is an infant carrier with base, which I put in between the toddler seats on either side. I'm guessing that you have 3 toddler seats, but maybe they'll fit since I'm guessing that an infant carrier base is at least as wide as a toddler seat. Or, I saw another mom's reply to you giving you links to toddler car seats that are narrower than most. It might be worth the investment to purchase narrower car seats in order to be able to buy a smaller, more gas-efficient car that is relatively inexpensive to purchase.
I assume you know this, but if you are considering a vehicle where you don't know for sure that all 3 car seats will fit, take the seats with you to the dealership and try them first before even wasting your time on a test drive.
If you are interested in a Matrix, I would strongly encourage you to check it out. I love it, and the hatchback has a suprising amount of storage space, plus the back seats can be put down for additional hauling capacity - either 1/3 or 2/3 of the back seat, or the entire back seat, can be put down since it splits to give you that option.
Good luck, and be sure to tell us what you end up getting!