Let me give you a few key elements at what the good old days were like. I know these things. I guess you could say I am one of these 'legends of old'. Just a rambling old man in the tavern that no one believes.
One thread that is still going today, updated to the boards when it first started, Unprepared Garen. Give it a search if you like.
Anyway, to the OP question. The good old days.
For me it was a lot of Player Concept and Fan Art.
The Player Concept forums was a much better place where a large group would come together to give each other feedback and ideas to create champions and kits that we would like to see.
It was a true community. Review for Review was a courtesy and helped to improve concepts. There were even community creation contests where people would constantly update threads and hold structured events where other forum goers would vote and the winner won, well, pride. Pride in the knowledge that other players liked their ideas.
The map Torrents Pass / The Flood Line was a massive community thread along with the aforementioned Unprepared Garen skin. Not just me, but a lot of good people helped out.
The Fan Art was similar to what it is today, but there was a time when people would go onto this forum to ask artists if they would draw their concepts for them. What did they earn in return of this service you ask? The satisfaction of helping out on a concept and see peoples responses.
The forums of old were often read and discussed and not just buried. Riot staff were very active during this time too.
But no one would believe this crazy coot. Hope that was a little insight of my experience anyway.
EDIT:
Here are the links to the mentioned "old threads". The text is there, but the images are lost unfortunately.
Torrents Pass 5v5 Map
Old Unprepared Garen Thread
This here is the New Boards Unprepared Garen thread I still maintain today.