Swords Dance +1 Question

So I stumbled upon the upgrade option for some skills like Swords Dance and even though it costs 500k and 200 EoW how much does it add? Thought these buffs were % based and so is it +5%? Seems like a little amount for the cost. Lastly how does it compare to the attack boost of PoD?

I did some testing, very little, but some, with claw + 1 and it about doubled damage. I used a Trunky and used snowflakes twice on the same fire monster, one with and without the boosted skill.

PoD, to my observations, only seems to give regular boosts, not upgraded supplementary boosts. In other words, PoD is better all-around and an upgraded supplementary skill is better if you want to get much stronger in a specific area.

EDIT: Did a little more testing, seems to be around 1.9-2 times higher than regular damage. Closer than 1.9 than 2, but still I only have a small sample size, so it's not concrete.

How does it compare to an non-upgraded boost?

Is say Sword Dance boosting damage by ~50% and Sword Dance +1 boosting it by ~100%

If it goes from 50% to 100% for +1 at +3 could it do 200% and effectively give underdog power to any monster?

I haven't done testing with regular boosting skill, and I will not as I would have to replace the advanced skills on my Trunky.

If it goes from 50% to 100% for +1 at +3 could it do 200% and effectively give underdog power to any monster?

You can only upgrade once, which I personally find logical.

A normal Sword Dance gives 50% boost to ATK.
A Sword Dance + 1 is assumed to boost 100% to ATK.
Since no one has Sword Dance + 1 , the assumptions are based on other supplementary skills that were upgraded by other people,

Cladun having Polish + 1
And me having Charge + 1.

I'd just get pod. Hahah.