Fixing 2nd gear requires pulling the motor and splitting the case. It's about as "involved" a repair as possible on the bike. If it only pops out on hard power now, in time it'll get worse and pop out with less and less torque and the dogs wear even more. If you're patient, methodical, and want to learn a ton about how a bike's engine works, could be a winter project. The parts aren't terribly expensive, the cost of having it done at a shop comes from all the labor involved. I've heard of people pulling their engine, then sticking it in a box and UPSing it to Sean(one2dmax), aka the official vmax guru. While you're in there, he can give you a true OD fifth, or an undercut gearset.
The "washer swap" is to give slightly more clearance for fatter tires. "Most" people don't seem to need this, I fit a 170 Metzeler in with no problems and a lot of other people have too. It's also not a great idea, since it shifts the wheel over a bit it increases the load on the bearings beyond what they were designed for.