Hmmm, methinks that like the clams, you must have been living under a rock for the Last few months
This issue has been discussed
ad nauseum with several possible solutions proposed, including:
a) Changing the cost of clams
b) Balancing water magic, so there's other attractive things to do with your water gems
c) Removing/altering the Wish spell, to remove the inevitable endpoint of a huge astral income.
Personally, I think dividing the value of clams by 3, as you suggest, is going too far. No-one would make clams that were that ineffective, IMHO.