So, has it been agreed what the optimum network settings are?
Short of switching to the LAN adapter, I've:
1. Assigned a static IP to my Wii that's >10 values higher than other computers attached to my router (like 192.168.1.20), by Nintendo's recommendation.
Nintendo recommends that?? Static IP is one thing, but the >10 is just plain idiotic.... oh wait, I see what they did. They're probably trying to make the advice idiot proof so someone doesn't pick 1 (likely the routers') or 0, etc. To bad most people won't be able to find their own IP address (on their computer).
2. Port-forwarded all 1-65xxx ports for my Wii's IP, set to "UDP" only.
3. Set my Wii as the default DMZ server.
Step 3 makes step 2 redundant.
4. Set my router for Wireless G connections at the minimum. (go away Wireless B, you're not wanted here)
B has all sorts of "speed issues" so to speak, and running in "mixed mode" you can be affected by them. So if you don't have any B devices, you should set it for G only.
5. I'm on Comcast Cable, and my MTU is set to 1500. Wiki mentions PPoE/DSL should have MTU=1492. (is there a reason to go slightly higher or lower?).
By setting the MTU correctly, your trying to avoid fragmentation (lets just call that bad for now without the details

). 1500 is your max MTU for the typical use case. By lowering it you can compensate for the overhead that may be added by your ISP (ie: PPoE). If you didn't lower it then the total would be over 1500 and you'd get fragmentation.
6. Manually entered all this and other necessary network values into my Wii's internet settings.
If you configure it statically then yes, you need to type in all the different numbers manually

7. I don't like Wii System Menu's "test connection" option, so instead I save all those settings, exit to the Wii Menu, then completely shutdown the console, turn it back on, then load the Shop Channel. I'm cool like that.
If you say so. You still need to tell it to use that connection, which I thought forced you to "Test it"
8. I disable all downloads and instant messengers, "live" programs like email programs, auto-updating antivirus (aka user-implemented sabotage), and Windows Updates.
Torrents are likely the biggest culprit for the general populus. The stuff you list isn't traffic heavy.
9. I also disable Brawl's "allow spectators" option, cuz I don't want the game saving and uploading unnecessary replays to the rest of the world (and I don't know WHEN the game decides to upload them either).
I've wondered the same things myself. What does participating in the spectator mode mean. I believe it's only for random non-friend matches, right? If that's the case, Nintendo might not need to send anything from your console (as those matches hit a central sever I believe - bah, I need to get a wireless PCI card, or a lan adapter...)
10. Hope that my roommate isn't using wireless interweb from his laptop, or talking on the phone. (i know for a fact wireless interweb interfered with sounds that were supposed to come out of my Wii Remote speaker during other games)
I'd blame that on the crappy speakers in the things... My remote is at zero volume from day one.