I'll post too, though with the same rationale that many have already given:
1) They should be worth the original amount because of the problems enumerated with nerfing. If you're concerned with overpowered or underpowered power-ups, leave ones with comparatively minimal risk and buff the rest.
2) If you keep the nerf, you have to reset the leaderboards, or they will be meaningless. If you reset the leaderboards, it would make them meaningless to a significant number of people.
3) I enjoy using Flame Notes about 75% of the time, pairing it with Bandmate or Jackpot evenly.
4) 9. I consider myself a casual player, but I care about my scores and use them as a motivator. I recently spent about a week playing through every song in my library to get moderately good scores on them, which I want my friends to see. I'm not doing it again!