Well, in my opinion:
You said you only need INT, but then you said you'd spam Holy Shock and Flash of Light.
When you've got 35k (or more) MP, and you just spam Flash of Light, which costs 300MP, then you'll probably have about 15k MP left when the battle finishes.
Also, Flash of Light heals for (approx) 4-6k non-crit.
And you can do (approx) 1 FoL every second.
On fights like Festergut, where there's heavy tank damage, you have to use Holy Lights, since the boss attacks the tank for 25k, 2 times a second. (Maybe not THAT much, but it hits really hard)
But then, if you use Flashes of Light on the raid, and beacon the tank(s), then the Priest's / Druid's / Shaman's AoE heals will go wasted, and they'll have to heal the tank.
So, in fights where there's heavy tank damage, the paladin should focus on the tanks, and use Holy Lights. (MY opinion)
When there's heavy AoE damage, the paladin should focus on the tanks once more, because his raid heals are not efficient.
BUT, he can be the only tank healer, so that the others can focus on the raid.
This still means that Holy Lights are better than Flashes of Light.
And something last.
On my pala, up until ICC came out, I used pure Haste/Crit items, and socketed ONLY +20 INT.
Then, a friend suggested that I removed some crit, and got some MP5.
I honestly believe that MP5 > Crit.
And I now prefer Mp5 to Crit, or even Haste sometimes, when I decide whether to roll or not on an item.
Made things a lot easier.