I just lost a whole writeup responding to your recipe.
Here's the short answer:
Add more base malt and corn, and not as much Dextrose (dextrin is something different, but I think you mean Dextrose by your usage in the recipe and the question).
The mix of grains is ok, though non-traditional. Traditional would be 6 row and corn (or rice). You might not get much flavor out of only 6 or 7 oz of the Vienna and biscuit.
I stopped using carapils/dextrin malt, as I find I get plenty of MouthFeel without it.
The mix of hops is also non-traditional. If you want traditional, stick with Noble-type or something like Cluster. (American Noble-type hops such as Mt. Hood, Sterling, or Crystal are great too).
Keep the IBUs below 20. Ferment it as cool as you can to minimize esters.
As far as an Dark Cream Ale, DO IT! It will be the counterpart to Am. Dark Lager that Cream Ale is to American Lager. Good versions of Am. Dark Lager can be REALLY tasty (ie, Full Sail Session Dark Lager).
I'd try Sinnamar and either Midnight Wheat or Carafa Special II (dehusked) to get the darkness.