I noticed that too... In the begining you got 1 point for every clam, now I can get 6-8 clams and only come out with 1 or 2 points...
and for the record I only clam dig while on quests that take me into those rooms, I figure I am in there for the hidden mickey, might as well grab some clams... self inflicted clam digging is not something I am in too....