Depends.

Since I am dealing with a S-corp, those returns would be amended, and amending K-1, which would in turn amend the personal returns (fed and state) of the owner (100% shareholder)

In the case of my client, yes, it is worth it.   The amount they might receive is greater than the tax effect on the owner's personal returns combined with my fees.

But since you are also dealing with PPP loans and therefore might not necessarily have a goodly amount of wages against which to use the ERC, the effect might be minimal on the corporate return. But, it would still need amendment.  And the personal returns, if partnership or S-corp.

It is one of those: have to do the calculations to deterimine the impact to be able present to the client to deterimine if it is worth doing. (dont forget to factor in your fees, which would then be deductible in 2022).  Almost a circular calculation.