I've softmodded my Wii to run HomeBrew software, and haven't updated the main Wii OS since, the changes are not that important, and if you wait for the new softmod to be avaibable for the new version, you can do it that way.
There is a very small chance of bricking, and the newer methods are very foolproof..
Regarding upgrading, Menu 4.2 :
- Deletes the Homebrew Channel v1.0.4 (title ID HAXX) and below and DVDX v1 (title ID DVDX).
- Now uses IOS70.
- Wii Shop Channel updated. Use WiiSCU or DOP-Mii to update the shop channel.
- Most of the IOS's have been updated or stubbed.
- Updates your boot2 to boot2v4, overwriting BootMii/boot2.
- Checks for region converted Korean Wii (checks for korean common key inside EEPROM?) if so then brick with a 003 Error.
- Improved region checking for discs and titles, the system menu now checks the Title ID from the TMD.
As far as we know, System Menu 4.2 adds no new functionality. No games, homebrew or official, require System Menu 4.2 to be installed.
In conclusion, just a bunch of checks to brick/restore your Wii if you are running softmods or homebrew additions.
And the next update 4.3:
- Deletes the Homebrew Channel and DVDX, title IDs HAXX, DVDX, JODI, DISC, and DISK.
- Now uses IOS80.
- IOS254 stubbed - BootMii is deleted.
- Fixed Bannerbomb less stupidly this time.
- Added IOS58.
- HackMii Installer Userland+Syscall IOS exploit removed
- ES_AddTitleFinish now checks the signature (Trucha Bug Restorer and similar won't work anymore)
So it only adds usb webcam support (IOS58) and more checks to brick/restore your Wii if softmods are detected.
So the last 2 major "upgrades" were just to brick/revert your wii if you were running a softmode/homebrew software, enough reason for me to stop updating the OS and enjoy the homebrew software.