For UK usage of brownie points as a belittling term, see
http://news.bbc.co.uk/hi/english/uk_politics/newsid_765000/765184.stm
yeahbut®
They were using this as an ironic pun on the politician's name, not, I think, as a derogatory usage.
The way I would define typical UK usage of this term is neutral in itself, but sometimes with an ironic context. In a similar fashion with another neutral term I might say:
"Margaret is very pretty" (neutral descriptive phrase)
or:
"Margaret is very pretty....!" (subtext: "but she's a complete airhead!"
The context will convey your attitude as to whether the brownie points in question are admirable or pathetically egregious.
