Pawan,
History tells us that no official from Google reads this user's group, so I'm sorry but your final missive won't happen.
As for your desperate needs:
1. You can do already:
- Go to the label
- Select All (use keyboard or the little select box)
- Select "All that apply to this conversation" (or words to that effect in the link that pops up)
- Delete... Done
I can't see a way to do that any easier without making it dangerously easy to do.
2. There is a task function that seems perfectly fitted to what you're requesting. I don't use/need it myself, so you'll have to check it out and see, but it certainly sounds right to me.
Hope this helps.