As a flintlock (CVA's generally have flintlocks that don't perform to high expectations), the rifle has a bit of added value. With the large 58 caliber bore, there is added value. The Spanish barrel, while probably accurate if in good to excellent condition, detracts from the value as most American buyers want the US barrel. The CVA Mountain Rifle is generally well regarded, but that doesn't bring in a lot of high dollar offers. Worth about $250 and it may bring in $200 to $300 depending on the buying market.
You probably have a very nice gun, it's just not in high demand.