You make some great points.  Responses to your points:
1. That's why I was thinking of only making copies of my own, or actual in-hand images - not screen captures.  I can totally udnerstand about others having copies of 'their' cels.  I think it might have the potential of lowering the value of the originals slightly because you could get a near-perfect copy for about 1/2 or less (depending on the cel).  Kind of like the legal right to make 1 backup copy of tapes or CDs.
2 + 3. back + time - you bet!  But isn't all art?  Question is if you want to make the investment of time to learn.  Once you learn, you'd be surprised how fast painting can be done - espeically on flat-shaded, line-defined things like this (compared to line-free art). 

You're right about owning the originals.  You'd never replace or be able to duplicate the exact nuances of painting on a cel; or the emotion attached to it.  I LOVE going to the DVD and finding the *exact* cel in the show!  I do it for all the cels I can.  But I really want to show off my collection visibly, pass them around to friends at the table, etc.  But that's dangerous to originals.  If you had near-perfect copies, you would really help people see this art as opposed to having them locked in a box.

Matt