I don't agree that you need to follow everyone that follows you. The idea behind twitter is that it is an ongoing conversation and having an ongoing coversation with 300+ people is impossible. If each one only tweeted once a day that is 300 tweets you would have to read at 2 seconds each is 10 hours a day just reading tweets. Instead as a nonprofit it is most important to follow your donors, supporters and volunteers and get to know them and they you. See http://oceangrand.org/tweet-tweet-nonprofit/ for more twitter for nonprofits.
We have a steady stream of people starting new nonprofits at Ocean Grand http://www.oceangrand.org. We start so many that we've never given it a thought on whether there is too many.
I believe the question is not whether to start one or not, but instead are you going to do the neccessary work it takes to make it successful. What we do not need more of, in my opinion, is nonprofit organizations that are not willing to put the work into making their nonprofit mission a success. I am contacted weekly by nonprofits who have struggled for years fundraising and grantwriting never getting successful enought to actually do the work they set out to do in the first place. The problem was they got the nonprofit shell set up but then had a hard time getting the support they needed to make it a success.
At Ocean Grand http://www.oceangrand.org we spend a lot of time "rebranding" nonprofits and equipping them with the information and tools they need to find the funding and run the organization successful. It is easy to set up a nonprofit but another challenge to get it successfully doing the work it desires to do.
We need more successful nonprofits and if a nonprofit is not prepared to do the hard work and work along someone that can help them make it successful, they should join up with one that is.
As a sidenote: We will work with a nd help anyone in the nonprofit industry that is having a hard time becoming a success to put in the neccesary work and strategies to rebrand and move on to doing the work they set out to do.