I am afraid you are 100% spot on. Whether the ground has loads of old timers from Maine Road or not, the reality is that many supporters in the Etihad have become somewhat complacent during the last 8 years. I remember the Spurs game you referred to and the atmosphere was astonishing. I remember the 4-2 against arsenal with the Adebeyor header, again incredible atmosphere - the game against Sunderland which we won 4-3 (not sure if memory is correct) and Hughes was fired afterwards - amazing atmosphere - the first few games against the Swamp dwellers at the Etihad in which I could not hear myself think...................since Mancini breaking new ground for city, the atmosphere has become dull and bland - and it is nothing to do with the corporates. Many of the fans seem to just expect incredible results all the time. I have sat in loads of places around the ground and always try to strike up conversations with those around me and so often, there appears to be abject underwhelming discussions, not necessarily harping back to the 'good old days' but generally unappreciative of what they are currently experiencing.
What about when Poznan came to town and had the whole stadium shaking with their 'bouncing' - which we then inherited for a while. As soon as other fans started to use it back against us whenever we were losing, we lost the will to keep it going. It was fucking brilliant and despite us nicking if off the poles, it was our thing and was a huge atmosphere pump and without doubt, all opposing fans were quietly jealous when we did the poznan.
Don't shoot me down, but the atmospheres at the likes of Anfield, Chelsea, Tottenham, Arsenal (most of the time), the Swamp and a few of the others, are consistently at a highly charged level in comparison to the Etihad. That is by no means just down to the fans inside the ground - outside the ground, they have managed to turn it into some kind of homogenised beige shopping mall - rather than ramping up the character of the surrounds to get a real sense of excitement.
I fear there is not going to be much change in atmosphere for several years and then only if City are performing right at the top levels in all competitions - the whole time. I for one, feel like I am walking into the ultimate dream every time I come to watch City. As a 53 year old, I embarrass myself by how overexcited I get when I see the likes of aguero, silva, toure and most of the others playing or even on the bench - and even back to the likes of adebeyor, tevez and Robinho. The feast on the eyes and senses just knowing that these kinds of players are at City, let alone having full blown man-love for the likes of Pep is beyond words. But it saddens me when there are bloody loads of empty seats all over the place and apart from the stalwarts of blocks 109/110 etc, bugger all in the way of atmosphere is coming from anywhere else. I just don't get it.