Sell Rental, Pay off our primary home??

[Josh Christians]

Here is my situation...
We OWN a rental property...currently trying to sell it.
The reason for trying to sell is that if we sell we can pay off our mortgage on our primary residence.
Can anyone tell me if there is any reason we should keep the rental and continue to pay on our primary home? Besides value of property value going up over MANY years?
Here are the #'s:
Rental: Get $500 a month after insurance.
Primary: Pay $400/month to bank.
I just don't see the point in keeping the rental just to give that $$ to the bank for our primary mortgage!
Appreciate any feedback!! I am fairly new to all this house stuff!