The BoA considered changing/loosening this rule recently (see: http://somerville.patch.com/groups/politics-and-elections/p/somerville-parking-rule-one-alderman-calls-unwelcomin63950d4353). I don't know how far that got, as my limited search just brought up articles about the start of the conversation, not whether there were/are any next steps planned. Worth a note to your alderman.

And while it's a pain (I also utilize street parking, but have an insanely nice downstairs neighbor who lets me park at the back of the driveway when I'm out of town for a few days), it should be noted that this isn't uniquely Somervillian. In the last few communities I've lived in both in MA and on the west coast there were similar rules in place.