For a limited time, Delta and American Express are offering increased welcome bonuses on their Gold and Platinum SkyMiles credit cards. This news comes shortly after Amex launched a new no-annual-fee Delta card. You can earn 70,000 bonus SkyMiles with the Platinum Delta card and 60,000 SkyMiles with the Gold. Act fast as these increased offers are set to expire on November 8, 2017. Using SkyMiles can sometimes be hit or miss, but one-way award flights start at only 5,000 miles. This summer, I flew my family of 5 round trip between LGA and CHS for a total of 50,000 SkyMiles. That saved me about $1,000, valuing the redemption at…