I have to be honest and say if I own a unit (even very old previous version) I generally will not buy the updated sculpts. (The only exception to this is chaos warriors and knights)
I have a tonne of Jetbikes, seers and swooping hawks and will not be changing them even if they are redo. I have a tonne of the old metal HE seaguard and phoenix guard not changing. I have old broadsides not changing them
By releasing new kits GW guarantee sales from current as well as new players
While updates and rescupts are nice, once a lot of players own a unit that's it.
I still like the current aspect warriors but they are not packaged well (other than DRs) with the need to buy multiple packs of 6 rather than boxes of 10