All links urls have a google page rank and alexa rating history. The more people explore and 'hit' those urls / pages is the more it's going to look better on your Page Rank and Alexa rating score. Meaning it's just going well for you since more and more people keep finding your page.
I'd like to talk about an example a website I follow every now and then. It's Ytkpro.com. Recently it's alexa rating has really declined to minimal levels. It should only be going up since they have a decent level of visitors on their forums.
I'll show the recent graph,
They got a new domain for their forums it seems and redirected old domain name, 'forum.ytkpro.com' to ytk.smfnew.com. This has made a huge decline in their normal hits for the real website 'ytkpro.com'. So it's going off the search engine charts as it seems while the other bogus domain name is gaining air.
It's like taking the life out of domain name. 99% of their traffic was linked to ytkpro.com through their forum.
Using two or more domain names isn't a bad idea. Proper way of using them is to redirect new domain names to the old and the parent domain name so that it stays up. Which is the point of SEO.
Have fun. :)