The snuffer is definitley worth it. I would suggest talking to Rick Bliss at New England Catamarans. www.new-england-catamarans.com He was the leader of the whole 6.0 fleet charge in New England several years ago.
The New England 6.0 fleet at it's peak had a local sailor make up some sweet carbon snuffer heads just like the old end pole heads the I-20s came with but without the angle. There might be some around still. Rick also sold a carbon pole out of a place in Boston that went with the head. We used the Skip Elliot snuffer bags. I think that whole set up came out to around a grand. You could probably get a cheaper aluminum pole but keep in mind that the 6.0 has a much bigger spinnaker than the I-20, F-18 and etc.
If your boat came with the New England style spinnaker or similar (around 350sq. feet) then you just need to have patches added. If it came with the Worrell style (around 450sq. feet) spinnaker it may be a bit big to snuff. I was going to try adding patches to mine but never got around to it. I did however use the New England Style chute with snuffer and it worked great and I was able to hold my own with I-20s downwind and even pass them in lighter stuff.
I have 2 pictures of my snuffer set up in this album.
As far as the self tacking jib, it's nothing I ever considered because the 6.0 jib is what really gives the boat it's power and really makes it an awesome ride on a reach. It would be convienent but you'd have to invest in a much smaller jib and lose lots of power. It would definitley be easier on your crew.
One thing I would look at is the picture of my jib sheet system. It greatly improves the friendliness of the boat without the crosswire if your boat still has the stock set up.
-Todd