I despise rule exceptions. Also, I am not keen on blocking for its own sake. So yesterday we played with the following house rules:
1. No card reserves.
2. During your turn you can take 3 gems of different colors, 2 gems of equal color or 1 SHIELD chip.
3. No lower limit on available chips for the action above. If there are 2 yellow gems, you can pick them.
We played 2 games in a row and we all enjoyed the game. Desirable heroes were very contested and nobody had the sour feeling that you get sometimes when a perfect hero appears right after your turn and you know another player will reserve it simply to prevent you from taking it. We do not consider that strategic play at all. That's simply luck. And we can deal with a bit less of luck in Splendor just fine.
But this did not turn the game into a multiplayer solitaire. The third house rule allowed for much more aggressive gem blocking and we were often pleading other players to hire heroes so that a certain color was refilled. Having a healthy roster suddenly became very important because gems depleted so quickly that you could not rely on them for your recruiting.