I have Stofens for my 430 and my 600. I don't really like using them. The colors/contrast I get from a bounced flash are much more pleasing. The stofen might be a little more useful on the 430 as it does not have a catch light panel but I still find it much more useful to just use the flash directly.
If you're looking for more interesting shadows, I'd use it off camera anyway...and I still don't use the stofen.
I'd recommend the 580 or 600 for the higher output and easier controls. (yes, it makes a difference in the real world). For example, when bouncing flash straight up to an extremely high ceiling, like the ones found in reception rooms, the extra power is nice. Also, when manually adjusting the output, the dials on the 580 and 600 are much easier to adjust quickly rather than having to hold down the center button for a few seconds and then pressing the +/- buttons, which are a bit tricky to press...minor gripe but it does slow me down a bit. I mainly use my 430 to light backgrounds or if I need the extra power for bounce flash...usually off camera.