Alewife is interesting, in that it was never meant to be a terminal station, but Arlington
that the train station would be near Arlington Catholic high school (and certainly it had nothing to do with the other end of the train line being in Dorchester, nosireebob) and no it couldn't happen and it didn't. So you have this inefficient terminal at the end of the line which works fine as a park-and-ride but also has to function as a walk-up station and bus transfer.
However, there are a ton of people who walk to the train from Arlington. Enough that I think it would make sense to dig up the field nearby (the tracks extend in to Arlington under Route 2), build a station and rail yard, and then re-cover that with a new field. It'd be in the water table, but would provide a much better end-of-line facility (the T frequently has issues on the Red Line related to Alewife) and would also shorten the walk for a lot of Arlington. Of course, they really should build it to Arlington Center. (And build bus lanes for the last bit of Route 2.)
As far as buses go, yes, you're right, the T doesn't have enough buses. Even if they got more buses, they don't have any more facilities to store them, and the only places to build more storage are generally out in the suburbs away from where you need the buses, so that means you have to pay to drive more buses empty to get to the people. The solution, in many cases
, is bus lanes, which can carry the buses more quickly so the same bus can make more trips and carry more people. But that's hard to do in America, because America.
[SGB we're going to hijack this thread and talk about transit planning, I'm afraid. And more to the point, to choose the color of the car they get to sit in a traffic jam in.]