Alewife and Wellington added density, but mostly in the wrong way.
Calling Alewife Bronxlike is a compliment it doesn't deserve. Yes, the "projects" are "edgy", but that doesn't mean we need the strip malls and utterly crap all around pedestrian access. Try walking from Alewife to the Fresh Pond cinema...it's the most ludicrous pedestrian experience I've had in inner metro Boston, requiring a switchback of what must be half a kilometer at least of unnecessary walking. Alewife Station is just a big parking lot that incentivizes sprawl in the Nortwest suburbs because residents can park there instead of dealing with the hassles of parking downtown, and no attempt has been made to make it anything more.
Wellington is only marginally better. A New Urbanist chimera that feels like a movie back lot built on the template of a subdivision divorced from arterial roads. It does nothing to gesture in the direction of improving its surroundings or really building an actual TOD.
These examples give me zero faith in metro Boston's ability to build TODs from scratch. The best that can be done is to build up existing nodes in piecemeal fashion. Davis and Porter should be built up to Harvard Square density at least; yes, new buildings tend to attract chain stores, but that blandness will fade over time (and don't forget that the demographics of Harvard Square are driven by adjacent wealthy parts of Cambridge and, well, Harvard people).
And obviously this is meant to be a gradual process. These businesses should not be simultaneously seized and redeveloped. I'm just saying that Somerville should incentivize this sort of development when possible and support it when proposed, and that Somerville residents should support it as well.