With Brown, the trend is important - and it has been down. (If I wanted to be really snarky, I would point out that per the most recent BG metric - the net favorable, Warren beats Brown - her net is 18, his is 17 - so she is more popular.)
This one they can't spin that Brown is more popular than Kerry - he has higher favorable and lower unfavorables - I think as low as I ever saw them. But, no matter the metric Kerry is most popular.
As to Warren, I really think many things you have written will be seen to be true. There was an article that shows that she was a Republican until her 40s - which I think means the Reagan era.
http://blogs.wickedlocal.com/masspolitics/2011/10/26/elizabeth-warren-ex-republican/#axzz1bx2rqThw This does not change who she is, but the people seeing her as the left's messiah will likely not see that see is a Centrist - as you suggested weeks ago - for years. This may not be bad news as it likely could help counter the far left image the Republicans are creating for her.
But, it may also be that Brown is self destructing - his campaign's whining that the LCV, whose only issue has always been the environment, is just helping his opponent and using dirty tricks. Somehow he thinks it unfair to call him on his votes that gave him a ZERO score.