To be Honest, I dont like the Purple. ^^
But, I dont have to like everything though.
I would still add stuff to the Surface though. while you have now a bit more variety over the overall biome. It still is a bit boring on the ShortRun.
Maybe the some "Boulder()" her and there.
Maybe try to Roughen up some Layers with a SurfacePatch that makes the topmost layer Concrete to air.
(Chould be done also with some Additions to the SurfaceAndGroundControl, aswell as some Replaced Blocks.
OOooooh, I Just got an Idea.
Add at the Furthest Values on SurfaceAndGroundControl (The Most Negative Range, aswell as the Most Positive Range) A Block you usually wont use in that Biome. (How about PinkClay, just as Placeholder)
That way you have the a good deal of Distance to the LavaSeas another SurfaceBlock. Which you can Tweak.
I would add 2 SurfacePatches with that Block as Source. One at 2-4 Blocks Higher than the AverageBiome Height. And 1 After that for two Blocks in Height.
The First one does Dirt:1 (Coarse Dirt), the next one Grass.
Then you Replace the Groundblock below the Second SurfacePatch with your Black Concrete, the Next two layers with Coarse Dirt (Where you had surfacepatch Grass) and everything above that also with Grass.
This should give you some Awesome Oasises in that Biome. Just Occassionally.