1. Are there any reasons why some developers/publishers don't release any bonus/goodies with their games? I don't expect they add a lot of goodies to their games or always provide some content (e.g. soundtracks) as free. But is it hard to add some wallpapers, avatars, artworks and similar stuff in their releases?

2. Are game goodies important for you?

I always liked having access to music from games. Manuals are a must, and many have more to them than simply how to play game. And having some art and concept pics to browse from time to time is a nice addition.

Bonus content was one of key features of GOG in the beginning. They were treating each game as a collector's edition, which meant full* game, with lots of free stuff.

*Full as in expansions included, no paid dlc, preorders, season passes and what not.

So why it seems this key feature is not very important anymore?

Because they have moved on from classical games, where a lot of the goodies where in public domain or built up over time, into new games where the material either do not exist or is part of different IPs (for example music)

Even wallpapers, artworks and avatars?

To be honest, I rarely ever see wallpapers or artwork still publicly released for new(er) games, unless it's in the form of Artbooks (which also seems rather rare).

So guess it has less to do with the feature being dropped, but just that those goodies seem to become less common with new release (as opposed to older games getting released around here).

Guess Publishers just don't see any reason to add / make them anymore.

Those goodies promote their games. I don't think it's a good idea to drop them.

I just need the manual, reference guide, map(s) and keycard - if the game came with those originally.

Because it feels like you have the original version/release?

Partly, but mostly because they're useful to have... if done well. For a complicated game that you might set aside for a month or two, it's nice to have that stuff to refresh your memory of the controls, how systems work, that sort of thing. RPGs are complicated enough that this is useful. Other genres can often get away with having only a Controls option in the game menu.

no
they are nice to have but when it comes down to it i dont care about them at all
i dont care about soundtracks
never listend to them outside the game dont care to do so either

I think I may be obsessed with game media (artbooks, artworks, avatars, icons, soundtracks, wallpapers and etc). I really like those stuff.

well different strokes and all that
i generally only care about the games everything extra is just extra but i dont care much for them

I have a Lara Croft statue that game with my copy of TLR. Does that count as an extra? What about my Pod Racer schematics? My NWN map cloth?