I think it may be best at 4
,
Deja vu cost being half the original cost of the card, rounded down, +1
.
So, of course, changing the ability again...
This means the cost of the ability and the card for a dragon is the same (at least for the unupped ones).
The extra splash of aether needed for TUing is too difficult for what you get from it.
So it makes it less useful for adding damage but more as a way to duplicate the ability.