Well here's another perspective.
My favourite shoe is the Inspire 6. I'm on my 2nd pair currently. No issues whatsoever. Yesterday I bought a pair of Inspire 7s and ran 6km in them last night. Today I can't even wear them about the house, such is the pain under my ankle bone. It feels like the high and tight heel collar has damaged or bruised the tendons there. Oh, and the kicker is that the specialty running shop where I bought them refuses to take them back or make good in any way. So $200au down the drain on shoes I cannot wear. Consequently I'm royally p*ssed off with this shoe and a tad sensitive about it at the moment.
The fact is I, and many others simply cannot wear the Inspire 7 despite loving previous versions of the shoe. OK, we're probably in the minority, but that doesn't mean our opinions aren't valid.
To the OP I say try on the Inspire 7, but be aware of others' issues with the shoe when making up your own mind. It may suit your foot and you may love it (and good luck to you, I hope it does), but lots of people other than me have issue with the high and tight heel counter which cuts into the ankle-bone region.
On the issue of similarity, clearly the Inspire 7 is a different, and much changed, shoe to the 6. To the extent where in my opinion other shoes are more similar to the Inspire 6 than is the 7 (my Brooks Trance 9, for instance). On the Inspire 7 the midsole dimensions are different (higher), the heel is firmer, the grade of foam different (more resilient and improved), the shoe is less flexible, the toebox smaller in volume, the last slightly different ( a tad straighter) so the little toe doesn't hang over the edge of the midsole, the lacing comes further up the instep and the foot entrance is smaller, the heel counter higher and tighter. The only carry-over is the wave plate (Mizuno's best feature, I reckon).
As for Asics, I've not tried 2160 but they've won an award in the latest USA RW tests, I have Kayano 17s and love them. Not as much as Inspire 6, though.
Dunno if that helps the OP, but I certainly feel better getting all that off my chest!
Edited: 01/05/2011 at 04:07