1. The airfare to TPE is quite cheap this summer. Go to www.angeltravel.com and you will find NW had one-way ticket less than $500. and you can get bonus mile because of your CO elite status. You can also go to www.eva-air.com and check the e-fare, many bargain fare from EWR for less than $850 roundtrip.
2. Since the airfare is so cheap, I suggest not using your mileage for reward ticket.