The big "problem" with non-aragonite sands is their uselessness. They won't release many, if any, beneficial compounds into the water that you really do want. Something like silica is pretty well inert (some chem types have argued about silicate buildup or somesuch, but silica remains in use for quite a few people), so its presence is only for bulk.
If you only want to add some thickness to your substrate and more aragonite is out of the question, you can go ahead. Personally I needed an extra couple of inches in my tank and I wasn't paying more than I already gave out for 110lbs of aragonite.. I ended up picking up a big bag of crushed coral to put on the very bottom in case I get a pistol shrimp who wants to burrow.
