Hey Kickstart.
The guys here are mostly correct about the supply being larger than the demand, especially since the advent of ebay.
However, if you have plates that are in really good conditon, they may bring a little more depending on the years of the plates.
Pairs of plates are usually worth more than single plates.
Also, sometimes if the plate has a certain series of numbers or
only three or four numbers or letters; then they can be worth more.
If you have several years of plates with the same numbers, they are worth more, sold as a group.
Another thing is that if some of your early plates are made of porcelain, they can bring a lot more money. I'm not sure if NY made porcelain plates in the teens but some states did.
Some states allow you to run model year plates. Like if you have a 40 ford, you can run a 1940 license plate. So again, if they are in good condition, they can bring more depending on who sees them.
Sometimes at a car show where they have a swap meet, the plates will bring a little more money than on ebay, however in the same vein, if you really have a plate or plates that are sought after, than ebay could bring you a lot more than you would have asked for at the swap meet. It's sort of a crap shoot.
But the guys here are right about ebay being a good indicator of what they are worth.
Good luck.