In terms of print quality and workflow and whatnot regarding a "real" RIP or the WorkCentre RIP, what matters is that your customers are happy.
I think there is a LOT of residual stigma about the bustled RIPs, because they used to suck really bad, but the current generations of them are just fine. The 76xx and 77xx RIPS as well as the 74xx RIPs produce very nice results. Not as many color controls as the expensive ones, but perfectly serviceable.
I have two 7675's which I use extensively, and I am completely happy with that decision. My only faults with the 76xx line as a print-for-pay machine is that the tray alignment is not nearly as easy to tweak as the DocuColor versions. (Of course NEITHER are as easy as the lowly Phaser line of laser printers, which have the best easiest-to-use tray alignment function built right in. I want that in the "bigger" machines!)
Mechanical capabilities of the WorkCentre 76xx are of course identical to the DocuColor 2xx.
Any time you have two machines instead of one, though, you have to remember that sometimes you can't split a large job between the two. There may be just enough difference that it isn't ideal. Then again, if your customers are THAT particular, you probably would have to have a DocuColor with an external RIP with more color controls ANYway.
Paper handling on the 6060 is of course going to be quite superior to the others. (2xx and 76xx would be the same in this case, other than the tray alignment thing I mentioned.) First-to-last color consistency is also likely to be better on the 6060, though I have always been very pleased with this on my 7675's. And, the 2xx and 76xx are likely to be equal in this regard as well, since it is an engine thing not a RIP thing.
Whether you need additional color controls of the more expensive Fiery or Creo or FreeFlow RIPs is a personal decision based on the workflow YOU prefer and the detail YOUR customers demand. In my opinion, in a "copy shop" type of environment, the WorkCentre 76xx RIPs are plenty sufficient.
And they're cheap!