Does exposing user to website activity feed without registration or login lower the value of website. Just imagine no log in page for twitter for illustation puspose.
That depends. Each case is unique. Encourage or force users to create an account can enhance or reduce the value of your website, but for sure just this point will not make your site be so much better.
Some projects, like Wikipedia, try to keep simple to receive contributions and do not really force you to have an account; but still offer a good user-experience for those who don't sign up. On the contrary, when Facebook started it was very exclusive before be what is today.
Please remember: this question should be more concerned with privacy and other technical issues of your project than "value" of the project itself.
Another resource for consideration is the 8 reasons users aren't filling out your sign up form
If you're artificially creating a barrier to use by forcing a user to register and log in, that user will pretty quickly go elsewhere. The existence of a sign up form does not intrinsically add any value unless the account that is created provides access to a service that a user finds valuable or provides a layer of security to keep the wrong people out.
User centered design would help you simplify the registration process to a minimum or to the part where the user is really allowing himself to be part of your community / service website.
Try to focus on delivering enough information to allow the user the benefit of the doubt, provide more content and when the user is ready to commit, then they can register.
This video was inspirational to me, and, it may be, inspirational to you too:
Edit: Given that reply, normally, the more amount of traction you get with your customers, the more valuable, on an end to end basis your product / service will be, as, the customers will establish then a more solid relationship with your product / service and may return later to purchase or keep subscribed to that particular or specific value add you will provide to them.