Like a couple of your ideas, heres what i thought for the three items.
Since its the "Watchers".
It would be neat if someone were to run through it, and first person to run through it as an enemy, will get marked, and it will follow them for X amount of seconds out of its vision range, but does not count towards that timer, while in the wards range.
Basically, you put it down, invisible ward. First enemy that comes through, will get marked, once that said champion leaves the wards range, itll do a vision tracking of said champion for a few seconds.
Since this is gold sight stone.
For each enemy that runs through it, whoever placed the ward, will get an extra 5 gold, can not happen again for 30 seconds or so. This could be abused by laners i guess, but wouldnt be worth trying to abuse in my mind.
This is the Tanky sight stone.
Only thing i could really think of for this one, is that you get an extra amount of XP for each time someone runs into the vision range of said ward. Now i dont think it should be aflat amount, i think it should be.. you get X amount of XP over Y amount of seconds, and this can multiply if more people come into its range (only works on one champion, so
cant run pat it 5 times and proc it), or even a small hp/mana regen instead of XP, to help heal you, but this could be very abusive.