I always felt crit rate and speed should be added to the Great hall
there are 10 lvls to great hall for each so in the case of crit rate it would be 1% per lvl to the max of +10% crit rate
speed would add 1 pt per lvl for a max of +10 speed at lvl 10
If you say this would unbalance the game and make it more pay to win. I would say to you that everyone has access to Great hall so spend your gold medals as you see fit
Unless they want to make Platinum medals for these stats, then I am sure more work would need to be done in plat arena to make it easier for more to access that
But I agree with OP in that something needs to be done for those who have finished Great Hall (I am not one of those)
The main reason to not include crit rate is because the more you add things like that, the less useful crit rate % gloves become. Even as it stands right now, they're mostly relegated to your secondary champs - getting crit rates of 60+% with substats and masteries is pretty easy right now. With GH CR%, you'd make that even easier.
They should not add speed in great hall. We knew a lot of players complaining (they shouldn't btw) that it takes years to max great hall, speed is king, etc., adding speed in great hall will add to their frustration.
Great hall bonuses is good as it is right now. What they should add is arena shop similar to bazaar, but uses currency gain in classic arena.