So you have a 10.1.3.* based ADF Faces application, and you are wondering if you should upgrade it to 11g and how.
To make the right decision, you first need to define to yourself what are your goals for the application. Here are some options:
You just want to have the application as is running on WebLogic instead of the old Oracle Application Server
If this is the case, you don't actually need to upgrade - you can just take the 10.1.3.5 application as is and deploy it to a WebLogic instance. A while back I wrote a paper and recorded a demo showing how to take an ADF 10.1.3 application and deploy it on WebLogic. And while the demo was using an older WebLogic - the steps still apply to WebLogic 11g. This should be the fastest way to get you to run on WebLogic without any code re-writes.
You really like the new UI capabilities of ADF Faces Rich Client Components 11g and want to take advantage of them in your UI
In this case I think you should consider a complete re-development of your application's UI layer. You can keep your Model/Business Services layer as is though.
Why? Well, the capabilities that ADF Faces 11g give you in terms of UI layout and user interaction, coupled with the unique capabilities that the ADF Controller's taskflows and regions provide, are a far departure from what you were able to build in the 10.1.3 days.
So to truly take advantage of those, you should really invest the time to design and develop with these new capabilities in a new way.
But my 10.1.3 application is too big to redevelop the UI in one go
If you want to take a stepped approach to 11g adoption you could have a hybrid application that uses ADF Faces 11g for the new screen, keeping the old screen "as-is" almost. The tricky part is that your old screen will need to be migrated to use the Trinidad components in order to live in peace with the ADF 11g in the same project. Trinidad is based on ADF Faces 10.1.3 and has mostly parallel capabilities.
For a basic introduction to the work involved read this migration of SRDemo document and pay attention to the link at the bottom to this page about ADF Faces 10.1.3 to Trinidad migration .
Now that you know what is involved you might have better data to make your call on the right approach for you. Note that it might be worthwhile choosing several screens from your application and trying the Trinidad migration and the complete 11g re-write to see what is the actual effort involved in each. This will give you more exact data on what is the right approach for you.