Forget the suspension if you are not doing two things:
Driving over rough terrain like the bumps
Powering all wheels
You speak of a "smother ride" and I really do not understand what it will benifit you. If you are concerned about your electronics mount them on a foam surface, or some other kind of protection. If you don't want to jostle the rest of your bot, well, almost all of the jostling comes from collisions, not deceleration from turning and stopping.
Also if your bot cam into any kind of pushing match it would distinctly be in the featherweight class. Not only will the omnis make it so that you well be easily spun, the 4 useless wheels will give you significantly pushing power. On your v1 thread you mentioned that you mechanical guy said he could put 75% of the weight in the center. I do not see how that is possible when you don't know what next years challenge is.
Here is one way to keep the chains in tensioned
http://www.flickr.com/photos/47595136@N03/4592232432/
http://www.flickr.com/photos/47595136@N03/4591612471/
http://www.flickr.com/photos/47595136@N03/4591612485/
Power the middle wheel run chain to the other axles, and then add a suspension to the angled bars with closed pneumatics.