If you register a domain with a registrar, you own the domain as long as you continue to pay the registration fees and abide by the terms of your registration agreement.
And yes, even though you are only paying $9.95 per year, your domain can still be worth $10,000. It's just like any other piece of property you own or own rights to, meaning it's worth whatever someone else would pay for it.
If you have a valuable domain that you could sell easily for $10,000, then your domain is worth $10,000.