There are a lot of people operating on the basis of old information who need to relearn DC residential geography. Part of the problem on the east side is that much of it was built out as completely uncontrolled post-WWII sprawl. Many of the arterial roads look like the worst of 1950's automobile centric strip development. Get a block or two off the main roads and you will find many nice neighborhoods, but the main roads present a poor first impression. They are gradually being rebuilt, but that is a slow process.
(2)Yes, Metro and MARC expansion would be desirable and could be done for a fraction of the cost of adding new lanes to the interstates. If need be, run the train down the center divider strip between the north and southbound lanes of 270.
I remain convinced that if we vouchered the schools and went to full school choice, gentrification (already rapid) would become an avalanche. People in the outer burbs are spending four or more hours a day in their cars. Adding a lane each way to 270 isn't going to relieve that pressure. It will only provide a temporary talking point for politicians who can point to the project and claim to be "doing something," but the new capacity will be completely swamped the moment it opens. Too many cars. And there's nowhere to park them once you do get into DC.
That surprises me. Of course, I left PG about 15 years ago, so I am behind the 8-ball as to the changes you are witnessing. But one of my 1st jobs was collecting loan payments for a finance company. Spent more that a few days in Anacostia. Dangerous place.
What about Camp Barry? And Stanton Road? Where are the natives being relocated; deeper into PG?
Some new pavement is needed, but it needs to be both strategic and placed with a minimum of expectation for solving the congestion. 270 should be three lanes in each direction all the way to 70, the interchange in Frederic where 70, 270 and 15 meet needs to be rethought (there is no obvious fix to that mess). The bridge for 270 over MD 85 is functionally obsolete for both roads. MD 97 (Georgia Ave) should be two lanes in each direction from Olney all the way to Westminster. Build the Brookville Bypass. That said I believe that more than three lanes in each direction is past the point of marginal gain for cost in increasing traffic flow.
While I think expanding service on the MARC Brunswick line would help, significant increase in service would require adding track to the current double track main line to prevent interference with freight movements. I doubt that triple tracking from Point of Rocks to Silver Spring is going to be that different from adding two lanes to the entire length of 270 from a cost or time point of view.
Extending the Red line from Glenmont station to the ICC along (or under) Georgia Ave should also be considered.
Unfortunately the only thing that would truly reduce congestion in the DC area would be to shrink the Fed Gov significantly.