According to my experience, RWD is good for SEO, here are the details:
1. Yes, google maintain separate option for mobile site however it als comes with a challange that you have to put different content in both the websites, which will be cumbersome and costly.
2. Mobile website having separate url which will require separate off page seo to get the things on top.
3. RWD is having trend, this wilk be liked by visitors and may try to surf pages, this will decrease bounce rate.
4. About heavy weight css or js, we can always compreass those files.
Regards
Krish
Www.ebiztrait.com