I use RW 4…even though there are a lot of snazzy and polished templates, the editing of the code is still the same as would be in any HTML editor feature (as in DW), so in the end, it becomes a lot like DW…
That said, anyone who is doing personal web publishing would appreciate its simplicity and “iWeb-like” user interface. Plus many of the add-ons are rather sophisticated, use php and javascript, without the end user needing to know anything under the hood beyond installing plug-ins. To really get to understading customization, eventually you get around to moving code around in the interface…so either way, some coding knowledge becomes par for the course (at least understanding basic CSS and html tagging).
Also, if your clients intend on maintaining their own sites afterwards (as in you designing a one-off site, for them to maintain), they would need RW, plus all of their plug-ins; my experience is that there is a learning curve to understanding where all the tools are installed on the computer (Library/AppSupport/Rapidweaver), while other assets like banner images (customizing) are not always intuitive, and require add-ons like the RW MultiTool. This is where iWeb IMO trumps RW for “non-techy” user-types.
If I were in your shoes, I’d look into taking a DW course online to advance your skills set. I have been looking into doing this myself with a self-paced online course through Lynda.com (not a plug).
Just some personal perspectives from a current RW user.