My Gen 1 is a 2010, and it was a little battered when I got it, but had next to no mileage on it. It is great for what it is, and I'm very happy with it. It's been great for the last year. I hope you are as happy with yours as I am with mine.
Bad tires are just flat bad tires. The tires that are on my Gen 1 will spin up on dry pavement if I'm starting on a hill. Mines an older one, and I don't think it has traction control. That said, it spins and spins on Seattle's hills. I haven't lost traction braking or turning, so there's that. The next set of tires sure won't be what's on it now.
You know that could be it too, I suppose that would offer a noise similar to an anti-sway bar that was loose. I recall taking a look at the rear control arm bushings and not seeing anything obvious but I never checked the bolts to check their torque. I will be sure to do that. Like I said this van has NO rear anti-sway bar.
I can't give you a fix but I can relay a similar problem I had with my 2014 C-Max. The C-max had a clunking noise coming from the RH front when going over a bump. The car was still under warranty so it went back to the dealer. After more then a week trying to find the cause of the noise the dealer replaced the RH control arm . Clunking noise was gone. Just so happens when replacing the control arm the recall for the door lock latches was also done. Year and a half later the clunking started on the LH side. Not as loud as the RH before it was repaired but sounded the same. The car is now out of warranty. Should I have it fix or live with it. My fix was to turn up the radio. My LH front exterior door handle wouldn't unlatch to open the door on occasion. This started to happen around six months after the control arm was replaced. Last fall I had enough of the door handle not unlatching. With YouTube's help I disassemble the handle and found the mechanic didn't install the handle completely. He didn't replace one fastener. After replacing the fastener and the handle worked every time. Now the neat part. With the handle be a little loose (you couldn't tell by pulling it) it was causing a vibration in the door that that sounded the same as the clunking control arm. Long story short, the noise may not be coming from where you think. Hope you find the cause.