No, everyone gets the buff.
Thanks for getting the numbers, i was trying to find them but couldnt...
Anyway, the first one is kind of nice in laning phase (it's a health pot and a 1.5 mana pots every base assuming you base ~3 minutes), but with how popular manaless champs are... But since the new regen items are % multipliers now, if you're buying a Chalice or a Spirit Stone that can actually be decent. But like i said, mostly only good on mages mid and mana hungry junglers.
8 AD is worth 360 gold, so it takes two dragons for the ADC to really get any benefit, and it's 360 gold worth of stats is less than 2 dragons are now (espiecially when you consider how freaking good ADC items are). Granted, it doesn't take up a slot, which is nice. 8 AP is only worth about 160 gold so mages don't care that much. And most tank jungles/supports don't have that great AP ratios anyway.
+15 MS is finally useful. i think the best thing to compare it against is basically a free 475 gold Alacrity enchantment for the entire team. Technically 15 MS is only worth ~196 gold since boots give 25 MS for 325 gold, but since it's the THIRD dragon everyone already has boots (and probably T2 boots).
+100 health is technically only worth about 200 gold, but it also doesn't take up a slot which makes it really good for carries. Usually i imagine Last Whispers will be done around this time and so ADCs might only have just started on the defensive items, so this is like half a ruby crystal in the meantime. It will also make GAs better on carries.
One interesting interaction is that since Baron will no longer give HP5/MP5, just a bit of AD+AP+out of combat MS+Tower damage instead, trading dragon for baron to get the 4th stack might actually be a decent trade because you'll be actually probably "better" at fighting than the baron team - and your buff sticks around.
Of course, once you get 5 buffs... it gets really crazy.
So pretty much, first two buffs are only marginally useful (ADC gets less than what they got before from two dragons. First buff is nice on mages and junglers. Third buff is really good. Fourth is actually not that great, but it is kind of a formality into The jungler himself gets a lot of out of all the buffs since it provides immediate stats that don't take slots, and junglers tend to use a lot of their slots with minor components + health pots + wards.
Fifth buff, of course, is insane 
