Well I am in Seattle (pretty much the same weather condition) and used to have Sienna LE AWD. VSC was a standard feature on the AWD so I can't say much.
But on our 06 Avalon Limited, VSC is standard and we hated it! The problem is when drive on snow your wheel spin and as soon as it happens, the VSC kicks in and start to slow thing down. When driving in snow (light, not deep) your car need the power to move out of the snow and VSC really stopping you to do that.
Near our house, there is a slop we need to go up in order to get to the main road. My 97 Camry without VSC has no trouble as long as I keep the gas stable enough (not too much power). On the Avalon, the car will slow down (in the middle of the slop!!!) and with all the beep, beep, beep from VSC warning, it took much longer to get out.
On newer model, Toyota finally have VSC button so you can DISABLE that feature. I would not care about VSC at all.
As for Toyota Certified, it usually cost $1000-$1500 more compare to non certified. It's personal thing but I can tell you a few years old car shouldn't have too many problems to begin with. I rather use that extra money to get an even "newer" car instead of certified but that just me.
I do suggest you to buy car from 'bigger' dealerships instead of just some auto brokers on the street. Just think about where the van comes from, bigger dealership usually takes used car from trade instead of getting it from aution. I have bough 3 cars in the last 9 months (all Toyota) and I got them from Lexus and Nissan dealership