It's one big difference between Boston/Cambridge and some other places like the Bay Area. You can get away from some of tthe really high real estate prices relatively quickly and a lot of the tech jobs aren't even in the city anyway.
There's not much to be gained by living in Fitchburg. The real benefit is that a commute from somewhere rural to a train station in Fitchburg (or the "end of the line" for some other city train system) is painless.
I guess it's just a function of overall population but it's nonetheless interesting that while Boston/Cambridge have indeed gotten very expensive, there's a lot of pretty reasonably-priced housing not all that far out.
I don't know. I work with someone who recently sold their house in Leominster (next to Fitchburg for those not from the area). He said there had been very little appreciation over a long timeline.
ADDED: The problem when these old small New England manufacturing cities gentrify is that you end up with a dozen square blocks of upscale and the rest is like it's been for decades. I worked in downtown Nashua for a long time and it was like that. Which, for me, makes it get boring quickly.