When my girlfriend and I hiked the JMT last summer, we relied on aqua mira drops. They don't leave any detectable taste IMO. We rebottled the drops, carrying enough to get us to Muir Trail Ranch, where we resupplied. Every morning, we'd wake up, and pre mix the solution (Aqua Mira requires a mixing of 2 solutions, and a 5 min wait time) in a tiny tiny dropper bottle. We still picked our water sources carefully, but would only wait 20 minutes after treatment before drinking the water. Although pre-mixing isn't approved in the directions, many of us do it just fine. Just remember, so long as the pre-mixed solution still has a yellow tint to it, then you're good to go.
Also, if you choose to do this method, remember the drop ratios needed for treatment. 1 liter of water requires 7 drops of Solution A, and 7 drops of Solution B. Hence, if you premix, remember to drop in 14 drops.
This system worked out great for us. I agree with others, most illness in the backcountry results from "Poop hands" and not dirty water. I think this is especially true since your group was using a filter, which is pretty much foolproof.
In regards to the bear vault...I too tried to get away with a bearvault 450. While it's possible, there are other problems. Namely, you have to pack the 450 perfectly to get it all to fit. The only problem is, reality dictates that you'll likely have to reach for that snickers bar, or powdered gatorade thats at the very bottom of the bv450. The time it takes to empty out the can, grab your goodies, and then repack perfectly was not worth it to me, so I went with the bv500. Don't even bother with the hanging method...it's pretty much prohibited on the majority of the JMT, and it's not fun to have to schedule your hiking mileage around your ability to reach bear lockers.
I bet you could get away with not bringing any traction devices at all, especially this year. But if you have your heart set on it, don't bring anything heavy duty, not even yaktrax or micro spikes.
Just pick up something like this: