I say no on Capital One. Here's what I would do, not just for your flight from EWR - SJD, but for any and all flights.
1. Go on Hipmunk
and check what airline has flights you want. If you want direct, then look for what airline has direct flights.
2. Get those miles.
In your case, UA, AA, US, and Delta all work. However, it is impossible to redeem via Delta; US requires you to plan way ahead and charges cancellation fees; AA is the airline with worst service. So I would go with UA. However, I must say I am biased towards UA, as I have sworn my loyalty to them. For travelling via UA, the minimum is 17,500 miles each way, 35,000 miles round trip. Since you have 27K points, 8K more should not be hard. Here are some options...
1. I would sign up for Chase Freedom if you haven't already, great card to keep, and gives 10K bonus with small spending req.
2. Sign up for one of the Ink cards that requires no AF.
3. Buy 8000 miles for $301.
Or just book one way with miles, and pay the return.