I'm going to be preparing my own speaker cables using this guide: http://www.audioholics.com/techtips/setup/interconnects/DIY_speaker_cables.html

1. Does anyone know if it is necessary or beneficial to tin the ends of speaker wire with solder before installing them either into banana plugs or as bare wire?

2. Would this prevent oxidation of the speaker wire?

3. Would it degrade the signal at all?

I wouldn't bother to tin the wire ends. I don't see any benefits; plus it will make it difficult to see the possible oxydation of the wire (it does happen sometimes). If you are so inclined, I would rather pretreat the bare wire ends with protectant/deoxydizer such as the CAIG ProGold, before installing the banana plugs.

Incidentally, if you don't need to connect/disconnect the cable frequently, nothing is wrong about connecting the wire ends directly to the speaker and receiver terminals. In fact, that way you will have two less metal contacts per wire to worry about.