What would the the average price be for this coin in BTC?
Would help if you can post what type do you have and its condition.
Is it worth putting it into a crypto exchange and earn interest on that, or should I keep it closed?
You risk of getting your funds locked/getting asked to KYC which is usually a total nightmare for reasons:
1. Support works at a very slow pace
2. KYC could be over the top which means your ID and proof of address may not be enough;
3. Complying doesn't mean you'll get your funds back, it is still within their discretion
4. No way to verify if they actually have set effective precautionary measures from hacking.
Holding where you have full control of your coins would be a better option if you're looking to increase its value over time but this is of course if you believe in bitcoin.
PS: you can move this to
Collectibles to get a better set of response