There are some strategies you can do here.
Use a responsive template that will adjust to the device (like I did on my blog at http://www.santry.com)
It is easier to share content within the same site, and you can structure it to work like an entirely different site. For example say you have the following structure
Mobile (hidden tab)
Then use two skins, one for your main home page for the navigation. And then just copy it, or use a different mobile optimized skin and in the menu control tell it to show hidden items, and to start the navigation from the root Mobile tab, by passing the TabID of the mobile page as the NodeSelector value.
dnn:menu menustyle="DNNMobileNav" runat="server" includehidden="true" nodeselector="xxx"
Structure will appear to have two different navigation (sites) that link to subpages that are all mobile optimized. In addition, on your main site your users will not see the Mobile menu option. Then within site redirection management just up a redirect rule to redirect mobile devices to your mobile site. Use a responsive template to handle displays for tablets and phones.
Since both navigation hierarchies are in the same site it then becomes very easy to have content centralization. Using this method, there really isn't anything you can't do in CE that you could do PE.