I have a Cosmic Mark II for sale, so you can decide whether I can be unbiased or not ,...but I definitely like the Mark II better.
The new features on the mark II shouldn't be shrugged off too lightly. If it was *just* the LED added, or *just* the gain switch, or *just* the better headphone socket, or *just* the cardas rca's, or *just* the improved circuit layout, or *just* the better wall wart, or *just* the variable position treble boost (and I think a better volume pot ?) , then I'd say the improvement might not be worth swapping. But add them all up and it's a better built, much more flexible and better sounding amp.
With the new version, you may default to using just the settings that were available on the old one ...perhaps the low gain, no crossfeed and no treble boost (which is how I've most often liked the HD-600's and ER4P's) ,...But, it's nice knowing that the other options are there. For example, it would cross my mind, *I wonder if this would sound better if it had more gain ? * ,...with the new amp, I can flip the switch and see. It turns out, it was best as it was, but I end up being more satisfied with the listen knowing that the *grass is not greener* .
You're basing much on an opinion (likely a very worthwhile opinion) that the difference between the new and old is 7.5 Vs. 7.75 . I'd say there's more like a full .5 between them sonically and I'd give the amp at least another .5 for it's added flexibilty and improved build.
On the Traveller bag, I'd say it's definitely worth it. The Cosmic is really not *portable* unless you have the bag. Unless the battery pack, CD player, amp, CD's, Headphones etc. can all be handily and easily brought along ...it just won't happen. Without the bag the portability is a perpetual possibility, but not likely to happen too often (which is a pity, because it's on the road that the sound really stands out ....I'm used to having good sound in my house, but not on the sidewalk outside ...).
Hope I haven't made the decision more difficult !
BTW,...for anyone interested, the Mark II Cosmic is on Ebay,...also an extremely nice Wheatfield HA-1 tube Headphone amp ! (a search should yield one or the other, then click on *see seller's other items)