Unless you cover the poles with a magnetic material (steel), the tone will not be affected. I don't know where the controversy can stem from. It's simple physics. If your covers are thick, it could force the pickups to be further from the strings, but that's the only way it could affect tone.
If the wires are working, you don't need to replace them, unless you think that they're so cruddy they might fail on you down the road. Since your p'ups don't have eyelets, be very careful soldering around the thin pickup wire. Work quickly if you can, so as not to overheat the wires. Tinning the new leads in advance will definitely help.
Adding a steel back plate will affect the sound of the pickup. It doesn't actually strengthen it, really, but it's doing something close. What it does is it changes the shape of the magnetic field and causes it to be more focussed - less spread out - which accentuates treble and upper midrange. It's exactly this effect that makes a Fender Telecaster bridge pickup sound so twangy, if you're familiar with that sound.
It might be interesting to try using a steel back plate on a bass. It would give a lot of treble and bite. I'm not sure if a production pickup has used one in the past. It also might be odd to use it with a humbucker, since the magnets are reverse polarity. It might cause things to get a little weird. It might be best left to the single-coil realm. I'm not really sure.
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