Seeing as now everyone can get a ward for free, there are many items that give hp (and "more useful*" passives), regular wards don't cause you to slow your build, is sightstone worth getting. I thought of this while playing 
support with some friends and bought seeker's armgaurd instead, then again I was also building ap for giggles did alright.
you have a title question and then a poll that are totally unrelated. ill try and answer the two questions as best as i can
AP Alistar: Ap alister is actually pretty good, but you would normally see that top lane. The issue isnt "is ap alistar good" the issue is, what are you trying to do and can you accomplish that with how you build him. If you are playing alistar for a frontline tank engage, then full ap is an exceptional poor plan. An item or two to make him pack a bigger punch, like a liandries or even just the zhonya's and a bunch of tank stuff could be really good...the zhonya could really mess with people when you come flying in pushing people around pop your ult then zhonyas all their ults.
I have seen full ad malzahar actually work..and top lane. The reason it works isnt just his voidlings, its because he built him for a purpose role in the game, then played him towards that role and did it well...he split pushed the snot out of top all the way to the inhibitor meanhile the entire team was pretty much losing elsewhere...but that got us in and we turned it around. Moral of the story...decide what you are trying to do in champ select, choose the best champ that does that, then build what you need to accomplish your goal and go to work. You might not carry with ap alistar...but your initiation will scary and force them to make mistakes avoiding you while your adc melts their face off.
Question 2: sightstone
It is still worth it on people that you would normally build a sightstone. Reason, why just have vision when you can have vision denial as well? there is no sweeper stone, so the only way to sweep wards effeciently is to have a sweeper..but then you dont get any wards out. So, the answer is:
Sightstone building roles/champions(usually support and jungle) should build sightstone and get a sweeper. Everybody else should get upgraded trinkit..if they want to get "vision denial" pink wards do that job nicely and then grant vision...with the trinkit you can just move your pink ward even if its still on the map (im pretty sure but if im wrong my bad) sweep the area and grant vision at the same time. Or get the upgraded green and drop tons of wards all around the map for the entire game. There is nothing wrong with just getting a sweeper and buying wards. upgrading to ruby sightstone...prolly not worth it.
Super late game however, it may be appropriate to drop the sightstone, switch to the green trinkit and buy a real item...if you are support, that is super super super late game..like 40-50 minutes. if youre jungle this could be a little sooner, but you never want to stop warding no matter how far ahead or behind you are...you cant let the enemy do whatever the hell they want without you knowing, if you do you can throw a game...winning or losing, you can still throw.
Sightstone is very much worth getting. It is more than just having wards. Sightstone lets you swap out for a sweeper so can start clearing the enemy wards as well. Also sightstone + pink ward basically lets you establish all the vision you need to take an objective on your own. Sightstone also recharges whenever you back, while the trinket needs time to recharge and generate the wards and also doesn't let you carry as many at 1 time.
Sightstone is pretty alright, wards on demand that recharge every b, so they're more expendable and free to use.
But as long as you buy wards, especially as the support (I buy 'em at the adc), to cover enough vision until level 9, I suppose you could get away with it. People should be buying more wards in general, but I have no idea why sightstone is the only thing enforced when it comes to vision (I have NEVER heard someone threaten to report another over an un-upgraded trinket).
can somone tell me why you would downvote a question about the game and how to play right? You trolls seriously need girlfriends or something to occupy your time...
Sighstone is for more reliable warding (no cooldown) and for vision denial, in the form of 
.
But, if you're not gonna get a Sighstone, upgrade your totem at least
Nope. Just take a mid lane AP mage, go "support" then don't buy any wards.
Damage>Vision
Giant hands aren't great for touch devices.
Someone on the team needs to have a sightstone, or at least buying wards consistantly. If the support doesn't build it and I'm playing a top laner that can benefit from the health, I'll build it. If we have a Lee Sin that builds it, I still build it as support because most Lees don't use it for vision, they just wardjump around the map.
I've considered just upgrading my trinket instead of buying sightstone, but having a sweeper is valuable so I usually don't.
Finally, I agree, you wouldn't have to build sightstone if everyone on your team would just upgrade their trinkets and actually use them, but they normally don't.
Giving everyone a free ward didn't ease up any of the warding responsibility from the supports, ha. Now we still get yelled at for 'not warding' even though we can only place 3 at a time.
I just realized that I phrased my post in a way that implies I don't think sightstone is worth building at all. Also I forgot to mention the asterisk. * more useful depending on how you build and play
Sightstone is a nice little hp boost early in the game. I find it combines well with a relic shield to make you tanky enough in lane to put real pressure on the enemy.
I think for 1600 gold it's definitely a worthwhile item for a support to have. Nice health and bunch of wards on demand for you to use. I think if the game drags on to the point where both supports can get 6 items(unlikely, but hey), then it's worth replacing the sightstone with something else, and just using the yellow trinket upgrade for 2 free wards.
Yes, sightstone should still be gotten on all supports. Use the trinket slot for the red trinket to deny vision of the enemy. If you are warding enough, you'll save money by building the sightstone. Assuming the sightstone doesn't give HP, if you ward 11 times, you saved money by having the sightstone.
To add on to another comment, even at full builds, don't get rid of your sightstone. Controlling vision is just as important then as it is early game. Keep the sightstone and keep the red trinket. If you have vision and your opponents do not, you have a HUGE advantage.
