If you downgraded your wii to 4.1, be sure you did it proper and did not leave an ios70 stub above your sm 4.1. Having stubbed system ios above your current system ios/menu can cause bricks. Anyway, there is not one single reason to update your wii to 4.3 or higher, it just limits the exploits available to your wii. A wii that is on sm 4.1 has every exploit available should you wish to use it (except tp), this is a good thing. If needed a wii on 4.1 can run bannerbomb v1, bannerbomb v2, out of region game exploits, etc. Updating to 4.3 provides no known enhancements to your wii and only limits what you can use should you wish to use. God forbid you accidentally ran dop-ios v11.3-11.4 on a 4.3 wii, the dop-ios bug is none recoverable on a 4.3 wii do to lack of bannerbomb. You really really won't to keep bannerbomb functioning on your wii, as this bug has been reported once on dop-mii v15, who knows what could happen. It is best to have as many contingencies available to you should you need to use them. Don't update to 4.3 is you have a choice, no one can list a valid reason to do so, 4.1 is where everyone should be.
My advice, never ever ever update from Nintendo. Update any ios/channels you need by yourself with dop-mii or other. Never install stub ios, never delete ios or sm.
To prevent your issue with the update notice, you should install priiloader. Once priiloader is installed you should block all updates, online and disc. Caution should be taken when installing priiloader, make sure your wii is online when doing this or delete the meta.xml from the /apps/priiloader folder. This will make priiloader install with ios36 instead of ussing ABHPROT, but ios36 needs es-identify for this to work. v0.7 of priiloaded has been reported to fix this issue, so you should be safe, but is it best to use the proven method of installing with ios36 if your wii is not online and avoid modifying your wii with ABHPROT just to be safe.
That is what I would suggest, keep system menu 4.1, ensure you don't have a stubbed ios70/80/90, etc, install priiloader using ios36 without ABHPROT, never ever ever update from N again.
Also, don't forget, everyone loves system menu 4.3, but no one has a reason for this love.