You've got the jargon down!
Here's some opinion:
upgrade from 11g to 11n only if you want to stream HD TV via WiFi. Even so, you'll be disappointed streaming HD on WiFi. Streaming standard Def. TV on 11g is OK if the signal strength at both ends of the link are very good.
Moving gigaByte sized files on WiFi, 11g or 11n will be frustratingly slow. So the case for 11n, IMO, is if you get it "Free" in newer PCs, then yes, get a $50 11n capable WiFi router - >if< your distances permit excellent signal strengths. Weaker signals make 11n no improvement over 11g and weakest yet, benefit from 11b.
If you have PCs connected by wire (ethernet) to your LAN, and if you do frequent gigaByte sized file transfers, AND if the storage system is Windows or a very expensive NAS ($500), then upgrade the PC to gigabit Ethernet. But a PCI ethernet card in an older PC cannot get much faster than 100BT ethernet.
Powerline Ethernet (like MoCA ethernet) rarely gets over 75Mbps. The switch built into the devices may be gigaBit, but the medium itself isn't.
Other WiFi in the neighborhood: Ideally everyone is on either channel 1, 6 or 11, none in between, to avoid the overlapping channels. What's important is NOT how many neighbors' SSIDs you detect, but rather, how active a neighbor is who's using the same or nearly the same channel as you. This is usually only key if the neighbor is streaming video on WiFi, or is a very heavy file sharing (bittorrent) user. If you suspect they are, simply move your router to a different channel- the client PCs will follow. A dual-band router is one way to mitigate having NO channels without heavy traffic, and that's very rare.
IPv6 - not a consumer issue for 10 years.
steve
