This is a curious activity - non-performing debt, i.e. notes not generating any cash for the holder and thus not extracting any cash from the ower, are being exchanged at market value, thus transferring cash via an intermediary (OWS) from a donor to the lender. This results in a non-cash accounting change for the ower and a boon for the lender. Economic activity is boosted if the lender's investment/consumption is more sensible than the donor's - ower does not figure into the algebra. This is likely to be stimulative if the lender's marginal propensity to save excluding risk investing is low.
If these are performing loans, on the other hand, the donor is, via OWS, acting as a market maker for the lender, providing them with liquidity/immediacy while granting the ower cash flow. This is like a stimulus payment to the ower (provided they consume the extra cash flow or invest it in risk assets). It's also a bail-out to the lender.
This is structurally identical to the Federal Reserve buying banks' assets, e.g. loans, and Washington increasing high-velocity fiscal spending. OWS's plan has the downside of being market distorting (via moral hazard) while the prior is less so (Fed's buying activity can be distorting if not done properly or if amped up to supplement Congressional inaction).
I came here expecting to chastise this but, economically speaking, it's a better use of surplus savings than having them sit idly in the money markets. It is, though, worse than building things, funding research, or helping feed starving children. Kudos, still, for beating par (the money markets).