c. some kind of decay in value of undug CLAMs over time
This already exists. If you dig and stake, your CLAMs increase by about 4% per month currently.
Assuming you have a sufficient number to actually stake, due to the lottery-style staking.
You can stake in a pool. I've been offering to stake for people
at no fee whatsoever (in order to try to decentralize the network from the current situation where JD has the vast majority of the stake), which will generate reasonably consistent
daily income.