As others have started to hint at, there's a massive amount of office/lab space around Alewife, and there's a lot of room for more development. There are huge areas, especially south of the railroad (north of Concord Ave) which could be redeveloped from one-story light industrial into higher density office and/or residential. Alewife is NOT a neighborhood like Porter Square right now, but if done right it may become one before long. (As an aside, there are plans, though I haven't looked at them recently, for a bike/ped bridge across the railroad to improve access to areas south of the railroad.)
An Alewife station on the Fitchburg would potentially generate three kinds of ridership - people who work in the station's catchment area, people who live in that area, and people using the Red Line connection to go elsewhere in Cambridge/Boston. Porter pretty much maxes out at two of those (with some university jobs north of Harvard Square spilling into the larger Porter catchment area).
If Alewife was added, there would be a need for some serious planning to determine if it would make a better "outer inner core" stop for long-range Fitchburg trains - i.e., the outer rapid transit connection where all trains stop, than Porter, or vice versa. Long run, if we move towards the Regional Rail model, one of them probably ends up as the major connection hub where trains from Wachusett/Fitchburg stop, or one served only by locals running shorter segments. Probably a good argument for Alewife if the area develops the way it's likely.
Also - there will be a need to completely rebuild the Alewife Station garage before too long - it's been said that current work is mainly to stop it from falling down. Perhaps one solution (assuming demand returns post-pandemic) is to build a substantial new structure as described above (on the Summer Shack site) which can take parking demand during reconstruction but also serve as a new connector between the Red Line and a future commuter rail station. The station needs better bus access as well (and could become a hub for significant bus service to the north and west with some minor bus priority improvements) which would open up a lot of potential transit connections as well.
Wondering if I'll see the Western Route double-tracking finished before I retire...
Photo: Melbourne W7 No. 1019 on Route 78, Bridge & Church Streets, Richmond, Victoria. 10/21/2010