In reference to live performances I think both styles have their plus points -

1 - It's great to see a favourite video look/dance routine recreated on stage

2 - Its great to see an old favourite re-worked.

It really depends on the artist, and what the majority of their fans expect from them.

When I see Janet I prefer the big performance number to be true to the original (AFY, Together Again, If, Alright, RN), but when I see Madonna I prefer the 'reinvented' version of an older hit (I definatley did not want to see the original Like a Virgin, Lucky Star or Erotica at the Confessions tour).

I think it's pointless to compare the two side by side as it's really down to what appeals to the concert goers for that particular show for that particular artist - classic or reworking.