In my experience, probably not. Most are low denomination stamps, like 1 to 3 cents, and are common issues. Generally speaking, most post cards have the commonly issued stamps, and not the commemorative issues, which typically are more desirable.
Your local library should have Scott catalogs, which is the authority for stamp collectors. If nothing else, you can use eBay to search "one cent George Washington stamp."
Generally speaking, stamp values are fairly low until you get to 1900 or before, but again, I am speaking in extremely general terms.
I am no expert, but I have looked at thousands upon thousands of US postcards in my life, and not once have I seen a stamp that I thought "that looks valuable."