Gotcha. The new interface is definitely rocking some grayscale.
In general I find that "simple things, done well" is a mantra that applies equally well to fine cooking, elegant engineering and intuitive user interface design.
I agree that Instagram's minimalism is alluring, particularly on a small mobile screen where pixels are at a premium, even at today's higher resolutions, if you're viewing pictures.
And I also agree that too much going on detracts from whatever individual experience you are trying to have in a given moment, whether it's writing a post, looking at pictures or participating in a Hangout.
Re: Twitter, fortunately we can still choose different Twitter clients. I'm liking Tweetbot a lot. I almost never use m.twitter.com