One thing you might want to consider is that you no longer have a license to run PL2 if you purchase a PL3 upgrade. I asked support about this recently when I noticed that PL1 was no longer in my list of purchased software in my DxO login, and they pointed at section 3 of the EULA to support this. Not brutally obvious IMO, and more restrictive than other licenses.
It still works in practice, but you may run into activation restrictions, and DxO can presumably shut down your old license key whenever they want.
Also discussed in this thread.