Main reason to get a standalone license in your case seems to be able to fly an N-reg commercially in the first place.
Other reason would be that a new 61.75 is required for each of the following reasons, all of which making the old 61.75 invalid:
- Address change (within 30 days of moving)
- English Proficient annotation (already mandatory)
- Credit card style license (already mandatory)
- Change of JAR license number (think UK/JAR to EASA)
- Possibility of FAA license to include photo in the near future
The standalone license also never expires and you can update all the things above via simple online system. New licenses are posted at very small fees rather than having to visit a FSDO and/or getting your license verified by the local authorities all at much higher cost.