If all you want a secondary card that you can use for statement credits, I vote you keep the Capital One Venture.
I have redeemed Ultimate Rewards points for a statement credit (hotel in a city with no chain hotels) and found it very easy. But since the annual fee is lower on the Venture Card, and you earn 2 points per dollar on everything using the Venture Card (instead of just travel and dining with the Sapphire Preferred) I would say the Venture Card is a much better long term card for statement credits, provided you don't mind using them for travel expenses.