Where the subway lines go makes a difference in terms of subsequent development (if paired with land use changes)
There is a great post at GGW, "In 1968, this brochure is how people learned about Metro," showing photo images (not scans, unfortunately) of a late 1960s brochure put out by WMATA to explain what Metrorail would be, where it would go, and what it would look like--the first leg of the system did not open until 1976.
According to one of the commenters, the brochure was distributed at an event on the White House grounds, where a mock up of the subway car was shown.
The comment thread discusses the proposed routing of the lines versus the actual routing. One comment is about the northern routing of the green line in DC, which originally intended to go straight up Georgia Avenue in plans, before turning east at New Hampshire Avenue towards Prince George's County.
Flickr photo of Columbia Heights by Otavio.
Instead the routing of that line was changed, in favor of stations on U Street NW and in Columbia Heights on 14th Street NW, as an economic development move, as these areas had suffered greatly as a result of the 1968 riots, which wrecked most of the city's "historic commercial corridors" (14th Street NW, U Street NW, H Street NE, 7th Street NW, 9th Street NW) that lay outside of the central business district.
This map shows the originally proposed routing.
This is the actual routing (Source: DC Comprehensive Plan, 2006, Transportation Element)
NW corner Georgia Ave. & Hobart Place, NW. Flickr image from 2012 by RockCreek.
The difference in the neighborhoods these days, between where Metrorail stations are, such as at U Street and Columbia Heights around the Metrorail stations, and on 7th Street-Georgia Avenue between Rhode Island Avenue NW and New Hampshire Avenue NW--a seemingly long distance but only 1.5 miles in length--is striking.
Despite the presence of Howard University, the stretch of Georgia Avenue without subway service languishes significantly, perking up at New Hampshire Avenue, where the Metrorail station is located, and then falling off again, as the rest of the corridor within the city lacks subway service--it's 4.1 miles up Georgia Avenue from the Petworth Station to Silver Spring, although the last 7/10 of a mile is in Maryland.
Park Place apartments at Georgia and New Hampshire Avenues NW.
Similarly, a mixed use building called Progression Place--some office, a bit of retail, and a fair number of residences-- constructed at the S Street entrance of the Shaw-7th Street Metrorail station (pictured below, image from Google Street View) has helped to anchor a resurgence of the adjoining historic building stock in the abutting area, along with the revival of the Howard Theater.
This type of opportunity is missed at many stations, including the other entrance for this station, on U Street at 13th Street NW, etc.
Some people argue that transit is supposed to be about transit, and that economic development justifications are a misuse of the program. I disagree for a couple reasons.
First, any public infrastructure, be it roads, ports, electricity and water service infrastructure, or railroads, subways, and other transit services are known to be "primers" that enable development.
Second, public investment should achieve multiple objectives and maximized return, given the limited resources government budgets have to work with. That most of DC's neighborhoods proximate to Metrorail stations are healthy or undergoing revitalization--compared to the state of these places in 1976 before the Metro system began to open--should be celebrated, not denigrated.