This is enough miles for free roundtrip tickets from the US to Asia and only a few thousand away from free tickets to Australia or New Zealand. Award tickets can also include a free stopover and even open jaw tickets (fly into one city and out of another) to maximize the trip. That could make the price of your award tickets be worth thousands of dollars, yet all you had to do was sign up for a credit card deal and spend a few thousand in the first 3 months.
This card has a $95 annual fee, which is not waived for the first year (as many do). 70,000 miles is a huge amount of United miles and definitely worth the annual fee in my opinion.
While I do not recommend going into debt (which can really affect one's ability to travel) taking advantage of deals like this has saved me thousands of dollars in airfare over the years, especially to destinations that tend to have high airfare costs (such as Micronesia). This credit card deal is valid until the end of July 2017.
Tip: I find credit card deals like this can really boost the amount of travel possible as the airfare is usually one of the largest expenses from a trip. I would say 50,000 or more bonus miles for an airline credit card is a good deal. Many will also waive the first year's annual fees.
These credit card deals are good to take advantage of if you have some large expenses coming up that you can charge to a credit card (home improvements, travel gear, cruises, etc.) which can easily bump you over the $3k spending requirement in the first 3 months.
If you've got the Delta cardmember bonus before through American Express, don't expect to get any further bonus, even if it's been many years later.