Anyone know if there are any quest that gives you spendable perk points as a reward? This seems like a fitting reward for a hard quest to me.

Don't think it is. It might be a quest that gives a special perk, but I don't know for sure(and I don't really need too know).

There are a couple of collection quests in the bards college that grant you mutiple skill increases as a reward, you have to find their instruments. It will likely give you a perk point given the number of skill increases you get.
Otherwise you could do the Haemoras (spelling?) quest, that is a garunteed 2-3 levels.

There are no quests for perk points. Perk points can only be gained from leveling up. Some quests will give you a skill boost or will add a permanent effect which you can check in the magic>active effects screen. But as I said none give perk points.

Haven't tried it, but it might be possible to lose enough skill levels via jail than re leveling enough of them again to raise a stat level.

From my knowledge you can't downgrade perk points in jail, you can only loose the progress till next skill level, but not a whole level for the skill.

You can get similar bonuses from quests, but they are specific and called abilities instead of perks.