I'm in the same boat although I'm on 3.2 softmodded, haven't used my Wii much since summer 2008. Nor have I been browsing these forums so I've lost touch with a lot of developments, hence my semi-newbie queries...
If I wanted to upgrade to 4.x I'm assuming I do not need to go out and buy/rent Indiana Jones or Smash Bros since I'm already softmodded so that gives me an advantage right? Or do these 4.x firmware nuke everything so that I would have to start with a real copy of said games?
The only reason I am even contemplating this upgrade is to play the recent rehash of Goldeneye. If grabbing cIOSes and IOSes via ModMii is sufficient then I will skip the firmware upgrade.