||I cannot see any potential negative to the inclusion of this information.
If I'm reading a customized cover letter and a candidate mentioned being a member/user/afflilate/founder/whatever of something in a manner that implied relevance - and I was unfamiliar with it - I'd certainly google it. Would everyone? No, but if even some do, it certainly seems worth inclusion.
If it were to somehow come up during the interview (I'd say it's worth bringing up if the interviewer doesn't) it would demonstrate passion and an interest in self-development - two characteristics of successful people in general. It certainly could set you apart from other candidates.
Interestingly, just from a recruiting standpoint for some non-technical roles, I've reached out to people and heard "I know who you guys are" more than I'd expected. I imagine the odds of someone likely to hire a TC member knowing of us has to be higher than in that particular candidate pool.
As to actually listing the rating itself, I'm not so sure I see much value to that but I'm interested in what others think.