I place great import on tweets. They may be fleeting in terms of immediate impact but if undertaken consistently they attract many non-human viewers. These viewers (search engines, scrapers [the good ones] etc) can have a major long-term impact on the diversity of places from whence visitors arrive, and therefore your visitor numbers.
I am more circumspect about social media bookmarking.
See my 'Using Twitterfeed' (
http://wizzley.com/using-twitterfeed-to-update-twitter-facebook-linkedin-promote-your-writing-1/) article for the answer to your question about 'tips for a large twitter following'. This is all natural. If you want to automate building a following then there are software programs that will assist. I have thought about using them, but have dismissed them for the time being - mainly due to time constraints and work-load.
