I had this problem before as a support but found it more productive to focus on items that would allow both players to survive in addition to working towards a sight stone, but if the lane phase ends, not much can be done with it unless you are Lee Sin or another ward-hop capable champion
though most of all, tank supports I found to benefit more from sight stone simply by the hp involved whereas mage playstyle supports are better by keeping vision in the only likely gank location from River
It varies by situation( such as if the opposing midlaner is an assassin, extra wards are essential) but most of all by play style and the champions involved
for instance, a sight stone will never hurt soraka simply because her only crowd control is delayed and situational, but if you are say Sona or brand or zyra or blitzcrank or other supports with aggressive crowd control (which is a large majority), playing to your champion's strengths tends to work better but varies by the opposing team composition(such as the rule of never going without vision against stealth/camoflage champions)
frankly put, I think the only reason sightstone is still popular is because of its necessity in certain situations as well as its former ability to light up the map. Even more frankly put, if someone messes up (any of 3 players): it's not the ward's fault XD