Sorry no answers, but just to say I am interested in this question too. I am a WP beginner who ended up using NexGen gallery because it seems the only one with both "photo album" for clients wanting a photo site, and "slideshow" capabilities suitable for clients wanting to decorate their articles and blogs. Plus very well supported with numerous add-ons. However I believe it's best to travel light. NexGen has 80% stuff I don't need, while the NexGen stuff I need is barely passable in quality. After my tests of all NexGen options I find that: (a) Only one of the NexGen photo album settings is "passable." NexGen uses mainly "lightbox" album displays which is not efficient to surf many photos. I prefer "highslide"--similar to lightbox but the visitor can click on other thumbnails while still viewing one large image. (b) Only one NexGen slideshow option is useful to me (although it is nice to have the others)--and there are no align or margin settings (though this can be done fairly easily using CSS hacks).
I.e., to avoid complications, I prefer not to have separate plug-ins for slideshows and photo album... NexGen seems the only reliable option for this combination. (Except for the $70/year/site Cincopa Video Playlist and Gallery. By the way, Cincopa's paid version is top quality but free version is totally impractical, with no way to adjust sizes.) Therefore, I am considering to get only one of many lightweight "slideshow" plug-ins, and forget about photo albums. For photo albums, clients can use Flickr. Or just posting photos manually is almost as well as using NexGen. Also I might be using Buddypress which has some photo add-ons that I have not yet studied. Anyway, after considering all this, I might just stay with NexGen if I could know more about:
1.) What if any are the problems with using the topheavy NexGen? (Evidently there are notable problems according to Francois!)
2.) Can unnecessary NexGen components be selectively removed to reduce its unjustified complexity? (Which seems to be what Francois is asking!) Thank you anyone who knows!