The progression that makes me happy is when it sounds like U2 have their foot on the accelerator. The vehicle is moving forward. Sometimes the foot is to the floor , sometimes it's just cruising, but it's going forward. As for 45 year olds after 25 years, I don't really see why that must steer them in a certain direction. It's certainly a factor in many ways, but that doesn't for example mean that they MUST simplify or become less experimental or whatever. Thats rubbish. It could of course happen, and may well be what has naturaly happened, but it's certainly not a rule by any means. Age alone is no reason for them to not continue to push the essense and spirit of U2 forward. I don't think creative inspiration tires. I think other needs and wants may though.
But, there are different levels of progression and different definitions. Sure, on many songs there are minor progressions. New sounds. New feel. New structure. New way of playing. Some we can hear and some I bet we don't even know about eg, what sounds simple and easy and not much of a change to us may have been a real challenge for Adam to get into, learn, work around and perfect and in that is his own progression, maybe what he would think of Song X as his most major progression from Album A to B and we may never know about that and just assume it was Song Y, which he'd pass off as a 'nothing' in terms of personal progression and evolution. I'm sure as a band as a whole their list of "Top 10 Experimental/Progressive Songs" would differ greatly to ours for that very reason.
Yes, a song like A Man & A Woman is progressive or experimental or new ground or whatever - minor in most ways, but progressive, new, yes.. I'm not saying it needs to inspire a whole collection of songs to be new to them. But I am talking about a larger picture progression in this thread. I mean there would be varying degrees of progression in different ways on every single song, but then there are the overall progressive umbrellas that tend to stretch over a whole album, and they aren't the minor progressions or new sounds or styles or structures from song to song, but the things that are driving the whole bands 'capital P' Progression. Not the lower case progression that simply makes Mofo sound quite different, new, unique to anything else they've done in many ways, not the least of which the other songs on that album, but the large scale progression that makes Mofo a logical and natural song on the road that has already stopped off and learned on the way and been intrigued further by some things and not others and has branched off from there in some ways but not others and then from something like Sunday Bloody Sunday to something like Bullet The Blue Sky to something like Zoo Station to something like Daddy's Gonna Pay and even Lemon or Numb to something like Bottoms (the Passengers b-side) to Mofo there is a progression in a larger sense happening there, and it's not as simple as what I describe there, as at each stage it is also taking in other U2 songs and songs and sounds and influences that are well and truly way outside U2, Chemical Brothers "Block Rockin' Beats" for Mofo as an obvious example. I'm not saying Mofo is those songs mixed in a blender at all, I'm saying it's an emerging personality that results in Mofo and that developing, progressing, emerging personality to me is what is rearing it's head again in a newer different way in something like Love and Peace or Else. Each time it's looking backwards into what it already knows, and forwards into something it's trying to understand and express. By the way, I'm not trying to say that that is the definitive line there for Mofo, just trying to give an example of what is the greater overall U2 progression versus what is the minor progression that also occurs all over the place from album to album and song to song.
The examples you name in Stay, Staring At The Sun etc are also good to use. The 'classic' U2 pop song written all over each of them, each definitely fitting under that umbrella of sound and feel and experiment that each of their accompanying albums has embraced. A Man And A Woman is that as well. Each of those three also displays a progression in that they sound nothing like any of the other 'classic' U2 pop songs that came previous, not just sonicaly but also in structure and in that each band member often displays in those songs a technical progression not heard before. They're not the songs that display where U2's greater progression is coming from or going, but great songs to display where it is at. Like test driving something over a familiar turf to get a decent but simplified taste of where in a few areas some of that progression is at. Promenade to With or Without You to All I Want Is You to One to Stay to Staring At The Sun to In A Little While to A Man And A Woman. There aren't ridiculously drastic differences there in that they are all fairly simple, catchy pop singles, but progression all through them certainly.
And I guess it's somewhere in between the two that you get a real feel for what is U2's overall progression. Man And A Woman in one sense is as all those pop songs from each album are - not a great place to hear where U2's creative front line is at that moment in time, but a great place to get a little taste of where they are at on the very, very, very surface of sound and feel. In another sense A Man And A Woman is quite a different little song in it's own right. I'm not denying that, nor am I saying I don't like it. I do like it. Quite a bit. But there are points in many of their songs that are progression, they are new in almost every way, but they aren't in themselves in the line of U2's greater 'capital P' Progressive path. They are just simply a fresh sound and progressive in that sense, while taking on board the sound and feel of what else is going on their on those albums.
Does that make sense?
As for what else I listen to.... all over the place. Really all over the place. Hard to say what is to my liking, I can't narrow it down at all really. My favourites are the things that are interesting, challenging etc. Last weekend I went on a bit of a shopping spree at the new local discount cd store, and bought;
Eels - Blinking Lights...
Ryan Adams - Cold Roses
Interpol - Turn on...
Cinematic Orchestra - Every Day
Turin Brakes - The Optimist
RJD2 - Since We Last Spoke
And that's not really an overall reflection of my tastes at all.
On Passengers it doesn't sound like U2 are skirting the borders of sef-indulgence....they've jumped right in and are up to their knees in it. 
