The only operational efficiencies are what I listed - back office stuff like billing, customer service, and advertising. You don't save any money on anything else because you'd have to maintain both companies' infrastructure as far as satellites, broadcast centers, and equipment for many years because switching customers out would be extremely expensive and time consuming (that's why Directv has waited so long to drop MPEG2 SD - even though they were down to ~5 million SD subscribers in 2013 which is half the number of Dish subscribers) By the time you could merge that infrastructure, at best you'd enjoy a few years of savings from a merged company before the business was no longer viable.
Yes you could charge more without any satellite competition, but only to the extent you are willing to lose everyone who has a choice. Directv is already the most expensive MVPD, how much more room for price increases do you really think they have?
I agree that the government would almost certainly let a merger go through today, since the competitive landscape has changed so much. That doesn't make it a good idea.
