Depends on what your goals are, IMO.
I like to compare the cam lift to the CFM ratings of the heads at the different lift heights. I haven't looked at CFM ratings lately, but I remember seeing some Vortec head numbers that were better than some aluminum heads up until roughly the .500 lift mark. After that the aluminum heads took over. That told me the Vortecs would be "better" for a low-mid torque "truck" cam, while the aluminum heads would excel with a higher rpm "car" cam. Make sense?
The above applies to either iron or aluminum heads. There are plenty of really good iron heads out there that will out perform a fair number of the cheaper aluminum heads.
In saying all that, figure out the true cost of working over your Vortecs to the true cost of getting a set of cheap aluminum heads going. Add up all the little nickels and dimes $$ that you are going to spend, and see what it is. Can you even get the Vortecs to where you need/want them? Are the aluminum heads actually noticeably better in the power department? Or will you be paying to just take weight off the front of your vehicle? Is it a big or small $ difference?
Just some things to think about.
