Having second card says that you are credit worthy and helps in improving your score. (blog.agentinsure.com)
So, we shall assume that your debts are credit card balance on first card is $ 2,500 with interest rate of 15 %; credit card balance on second card is $ 600 with interest rate of 12 %;; student loan debts $ 25,500 with interest rate of 7 %; while auto loan stands at $ 8,000 with interest rate of 10 %. (myfinancekits.com)
I believe that from my combination of Chase Sapphire - United Traveller (40,000 +30,000 +5000 for added second card holder = 75,000) I'll have 15,000 miles that I could use for the second ticket too since a round trip to Europe will be 60,000. (milecards.com)