My parents purchased a $10,000. Whole life policy for me in 1956. What could it b worth?

It could be worth nothing - if they stopped paying for it. 

I cashed in the $10,000 policy my parents had purchased for me. The payout was only $1700. I am sure every plan is different.

$10,000.  Unless the savings part of it is more than that, in which case, you can take that.  You would have to READ the policy.  They are not all the same.

If it was paid in full when they purchased it, it could have some considerable value. The amount would depend on the rate of interest. However, if they purchased it on a payment plan and the payments ceased years ago, it's probably worthless.

A $10K policy is worth $10K.  They are worth what was purchased. IF the company is even still in business. You should check on it. 

It could be, and probably is, worth nothing, because life insurance policies require ongoing payments and don't last for 65 years if you don't keep paying.

$10,000 if you are the beneficiary. Just call them, they will tell you. 

Go ask an insurance broker or the insurance company to show you the calculations for the accumulated added value. This could be a significant sum.

If it's fully paid for and still in force, it has a $10,000 death benefit to your beneficiary should you die.  (Have you named a beneficiary?)

Do you mean does it have cash value for a redemption or a loan?  That's possible with a whole life policy, but you'd have to look at the policy to see if it has a cash value.  If you can't find the policy but know the company it was with, you can probably find a phone number to call for information.

You need to contact whoever the policy is with and they will be able to tell you.  Depending on the terms of the policy it may be worth $10,000 or it may have grown and compounded and be worth more.  None of us can tell what the terms of the policy are.