Walkability is incredibly valuable to me (the ground floor of my building is a grocery store), but I'm not sure that the new downtown silver spring is what most people have in mind when they think about "walkable" neighborhoods, if I recall correctly it is mostly chain restaurants and clothing stores (besides the theater and seasonal ice skating).
If one of you is metroing and one is driving, or if you both regularly take the metro then downtown makes sense and the extra rent is worth it, but if you are both driving on a daily basis then saving the difference makes sense. It's almost impossible to call two apartments "otherwise equal" if their location doesn't fit your lifestyle: for people without cars downtown is the only reasonable option and for people who drive everywhere paying for parking and dealing with traffic downtown is a terrible idea.
Edit to add: I didn't intend to sound snarky about silver spring. What I was trying to say was, from my perspective walkability means able to walk to work, social events, and necessities, and no standard walkability metric will be personalized enough to reflect your priorities.