Exactly ! I would do it like a the logic of a lod system.

create 4 step graphics for %25, %50, % 75 and %100, then you could still do a bit of scaling also. But no more the %25(+- .25) before changing steps. So if you are at %0 zoom you can scale down the quad to atmost scale = .75. Then change to the next step graphic and scale it up top scale =1.25; . That step can be scale all the way down to scale = .75 before changing the next step image.

This gives you a smoother none stepping zoom and reduces the blur and jaggs

Mal