34f -- I don't know where you got your employment figures from -- but there's a problem with them -- Cambridge was a major industrial city -- Kendall square almost certainly employed many more people in its heyday that it does even today
Click the link! It goes the City of Cambridge website (developed by the useless Community Development Department using stupid data that could've organized itself).
Under the "Cambridge Workforce" section are 3 documents that answer exactly the questions you're interested in.
In 1967, there were 2477 establishments and 65798 workers, 25028 in manufacturing. In 2011 (the most recent data on the page) there were 4445 establishments and 105628 workers, 2775 in manufacturing.
So yes, there was a 90% drop in manufacturing (good intuition), but there was still a 60% increase in workers in the city. So we lost 22,000 manufacturing jobs but gained 40,000 jobs over the same period, meaning Cambridge added 62,000 non-manufacturing jobs from 1967-2011. Judging by the success of the past 5 years, I think it's safe to say we're even higher now.