Regarding the pool full of sharingan eyes, thats probably to show these were Sharingan eyes, rather than normal eyes floating about...
Kakashi and Obito, you realy only see Obito with his eye on close up when Sharingan is active as during normal time, its just shaded, so there is no evidence it's still active, or can you prove it? also regaridng Kakashi, wouldn't it make sense he's just covering his scar? and only unveil it when he's about to use it? although it's a valid theory, one can question if it is infact correct, as both these people have never showed their eye, it's always somehow covered... if you think, but hey, now he always have his Sharingan on, it is because they're locked in combat during the war, so really no point in turning it off?