Okay, I have one question for someone who understands this better than me. Lets say I register dropped domain pr5. I redirect it to my normal site. Does that mean that all links that point to the dropped domain will now bring link juice to my normal domain ?
I would have to disagree here. What that means is that the traffic will go to your other domain, not the link juice. The links are going to that PR5 site - therefor the link juice is going to that PR5 site. If you want to push some of that juice to your other website then you need to host the PR5 site, put some content on it, and then put a link on that page back going back to your site. By doing this, the PR5 domain is getting juice from all of it's backlinks and then sending that juice to your site. The less websites you have linked to from that PR5 - the more juice that will go to each linked site. So, if you take that PR5 and develop it, then link it over to 1 site. That 1 site will be getting more juice than if you were linking to 5 sites.