RAW files would complicate my post-processing workflow
If you're already converting your JPEGs to TIFs during the editing process, chances are you are converting them back to JPEGs at the end of the process. Starting with RAW and ending with JPEG actually removes one file conversion. And the non-destructive editing with Capture NX2 (and Lightroom), means that you wouldn't need to save the intermediary TIF created from the JPEG.
To be honest, I often convert edited RAW files to TIFs to perform special tasks that I can do only with Photoshop or occasionally with ACDSee Pro. But that's just how I work.
Working with RAW does mean learning new software or at least additional features of your current software. However, once you’re comfortable editing RAW images, I’m pretty sure that you’ll feel that the effort was worth it.
That’s not to say that you will always need to process the RAW files. In cases where you are planning just to post certain images to Facebook or email them, then making leveling and other relatively minor corrections directly to the JPEGs (accepting some loss in quality), makes perfect sense. However, if you are trying to “recover” an image that wasn’t exposed correctly (or the way you wanted), I believe that you are far more likely to be successful if you work with the RAW file.
Here's a JPEG produced from an unedited RAW file.
And here's a JPEG produced from an edited version of the same RAW file with some D-lighting, added saturation and few other minor adjustments.
Workflow is really all about personal preferences, so I'll have to say the jury is out on this one...