I was not going to reply at first but I guess I will now I have had a few hours to think it all over and form some coherent thoughts, the end result may be lacking somewhat in length but hopefully it will convey my thoughts.
First up I completely disagree with the original poster, sure releases on the GBA have slowed down (the console is coming to the end of it's life after all) but many things are still happening:
For instance a bunch of high profile, high quality translations are nearing completion/coming along very nicely:
Fire emblem:
http://community.livejournal.com/dtn_fe6trans/
Gyakuten Saiban/Phoenix wright
http://comebackcourt.sourceforge.net/ and Mother 3 to name but a few, there are many more interesting GBA hacks and translations floating around too if you look but these are three good examples.
So releases/release groups are an important part of the "scene" sure but many seem quick to forget they are not the only thing that make it up, sure the groups are less personal than Amiga/Snes/C64 days but since the MPAA/RIAA and other fun groups like that (does anyone know who, if anyone, does roms/isos of games by the way?) are now sporting, and all too eager to use:
http://www.theregister.co.uk/2004/01/13/ri...amilitary_garb/ , black ops teams who can blame them (saying this a fair few anime groups are still pretty personal/high profile so I am tempted to say release groups are not even making the effort).
Oh yeah no person has yet mentioned trashman, sure they may not be a "group" in the strictest (insert snide remark about elitist types here) sense of the word but they are responsible for a fair deal.
As for homebrew, the DS has seen some wonderful things and the GBA has not been bad either.
One thing to remember the roms from the older consoles are still illegal so not all homebrew is unquestionably legal: copyright is many more years than has has passed since their release when you talk of older games.
As for the gbatemp and ilk "bringing the scene down" comment I say while I am fairly fed up of answering which cart is best (come on people do you think we would all be using different ones if there was a decisive leader), how do I play F.E.A.R. (or whatever the popular FPS of the day happens to be) on my GBA, I demand an emulator/rom released 5 mintes ago/rom of a game released 4 months from now/translation of a game from Japanese to Klingon (even if the game is out in Klingon in 2 weeks) type questions there are countless interesting posts from people all over on pretty much every subject that anyone could possibly care about. I may not have been into the "hardcore" IRC,BBS stage but (normally I got stuff from those that were so only ever got over the shoulder type glimpses) I will be damned if they could match the shear wealth of experience/diversity found in these sorts of places. Even better there are no really disparaged sites any more, places like high-society (probably not the best example but still, places like gameboy-advance.net exceptyed).
Sidenote, for anyone reading this who may be considering such a question
http://anonym.to/?http://fun.drno.de/flash/posting.swf is for you (others may wish to have a look too as it is quite funny)
Which brings me on to my final point: keep intro's the hell away from me, if you want to make a demo go for it: I will keep it on my cart/computer and show it to all family/friends/random prostitutes I meet out on the street (I do genuinely have the shit faced cows demo from a little while back on my cart right now).
Code a trainer and stick a nice intro on that by all means too.
Then again this is just my opinion, others may (and going by this thread do) have others.
To end I shall quote Trashman's NFO: "for teh gamers, fuck teh lamers"