Should I take baby aspirin even if already on plavix (clopidogrel)?

Probably. It depends on the indication, of course. Stents, especially drug eluting stents ("medicated" stents) which are one of the major indications for plavix, (clopidogrel) require dual anti-platelet therapy, thus Aspirin is routinely given with Plavix (clopidogrel) and Plavix (clopidogrel) alone is inadequate and risky.