Light rail, whenever mentioned as a potential transit scheme, is usually mentioned as a tool of economic revitalization and/or development; densification as well. Held up as one of the prime examples is Dallas' DART system, which has seen several Transit-oriented Development districts. The largest and most widely known of these is Mockingbird Station.
After contacting the American Public Transit Authority, I obtained several copies of various light rail studies, including one, The Initial Economic Impacts of the DART LRT System, which analyzes the economic impact of LRT, and is very helpful in identifying confounding factors in analysis of LRT system effects, including highways, decentralization, relocation costs, changing economic structure, and local public policies.
The study found, using property values data, that in 11 of the 15 areas surrounding DART LRT stations, property values increased between 1994 and 1998, and that the jump in total valuations around DART stations was 25% higher than in control neighborhoods in other parts of the DFW metroplex. Along with this, when looking at land values, average appreciation around DART station was twice non-DART neighborhoods.
Therefore, one can see, at least in one aspect of "quality of life", LRT has a quantitative positive impact on its surroundings.