No
It is not possible to move your WiiWare and Virtual Games from one console to another, as the information is tied to the actual hardware of the console.
Only Nintendo itself is able to move your WiiWare and Virtual Console Games to another brand-new Wii system during a repair or in case of a replacement due to theft.
The Wii VC games technically shouldn't obey the Wii sound settings because each game is suppose to be a direct port which is ran on top of an emulator. To my knowledge, the hardware for most (if not all) of the consoles that are emulated on the Wii did not have a stereo/mono option.
Instead, the Mono/Stereo output was controlled and toggled from within each game. As an example, I seem to recall the Final Fantasy games for the SNES had these settings in their options from within the game play menu.
I never played Super Mario World much as a kid (didn't own a SNES :( ) but Nintendo has always tried to spot-light the quality of their new hardware by the release of a few games that integrated most of the new technologies provided by their new hardware.
I think the SNES was the first Nintendo console to use stereo sound. Since, SMW had stereo sound, I doubt there was a way to cut if off because Nintendo would have wanted to show off the systems audio capabilities.
SOLUTION
Sorry for taking so long to respond to this with, um, an actual solution but there is a hardware way to fix this.
Plug your left and right audio RCA cables (which I assume you are using) into an RCA splitter. You can then plug your one cable into your working TV channel and you will get both audio channels to play through the one speaker.
Here is an example of what you are looking for. As you can see, these things are dirt cheap, and if shipping isn't an option, you can probably find one in a local Walmart, Target, RadioShack (or international equivalent.)
I actually have a couple of these splitters and they were necessary in my childhood because I only had a mono-input TV in my gaming room. I actually daisy-chained some of them because I had a bunch of gaming systems as a kid and I didn't have a multi-input box. To much daisy-chaining will degrade the quality of the sound, but I'm guessing with your setup that's not going to be an issue.
Best Answer
No, it does not.
Nintendo currently only sells a small fraction of the Virtual Console titles on the Wii U as they are converted to Wii U for controller compatibility and other reasons.
You can still purchase these games on the Wii U from within the Wii virtual machine environment via the Shop Channel and Nintendo is still distributing games for the Wii through this shop (including some of it's Club Nintendo giveaways).
It is very unlikely that many if not most of these games will ever be ported for native Wii U play due to the radical change in controller schemes. All Wii U games are required to support the tablet as the primary controller.
As for the second part of your question, the only significant game I am aware of that will not transfer to the Wii U's Wii emulator is Lost Winds. I have also found anecdotal evidence that DLC for Final Fantasy The After Years fails to transfer as well and neither can be downloaded from the Wii Shop Channel on Wii U.
One added note as this was touched on in comments. Nintendo has indicated they will re-issue an unspecified number of Virtual Console games on Wii U and if you have already purchased the Wii version and it is linked to the Nintendo account you transferred from a Wii to the Wii U, then the new release will be offered to you at a greatly discounted prices ranging between $0.50 to $1.50 in the U.S. (if you did not transfer your Wii profile to your Wii U then you are not eligible for the discount).
Correction: In April 2014, Lost Winds became transferable from the Wii to the Wii U. To transfer it you will need to have held onto your old Wii system and repeat the transfer process. Otherwise you'll need to repurchase it.