I'm not pretty sure that this is the best way to do ajax updates but definitely having only <AjaxZone> taggs is not an option to me.
Have any Ideas or Recommendations - don't doubt to share...
Take a look at RichFaces (http://www.jboss.org/jbossrichfaces/) or ICEfaces (http://www.icefaces.org). These are both JSF component kits, so they will require a JSF implementation (MyFaces or Sun RI). Both of these work nicely with Seam. Others have also had success with Oracle ADF now known as Apache Trinidad.
If you want your Ajax request to result in an updated server-side tree and very fine-grained updates to the page, your best bet is ICEfaces. I like both RichFaces and ICEfaces, but ICEfaces is unique in that it uses a diffing algorithm to only make changes to the page that are actually changes. You don't need any of those "zone" tags because it automatically figures out what to update.
The beautiful part about using Ajax-based JSF components with Seam is that you don't do anything differently than you do with a non-Ajax application (talking in general terms). Seam doesn't really know that its components are being used over Ajax, so you can do all of your normal authentication, authorization, long-lived application/request/business process/transaction, stuff. The key is that you use a long-running conversation to keep state from one Ajax request to the next.
I cover this question a bit in chapter 7 and chapter 12 is totally dedicated to this topic.