Playing my first MP game as TNN

[Baalz]

Eh, I don't know, E9 is far from wasted. You're mistformed, yes, but you also only have a couple points of regen so the frequency of blows which cause damage is a very important consideration. Assuming you're also dropping barkskin you'll be fine against spear wielding human infantry but you start running into trouble raiding nations with good PD (wielding swords, pikes, etc.). If you do that against a good player who notices you've only got 2 reinvig then your raiding can be seriously hampered by just pumping up PD. Sure, rainbow armor is a great addition, but it also greatly increases the cost if you are trying to put it on each raider in early game. E9N4 (along with alt research) will let Sidhe Lords equipped with a frost brand and vine shield take out essentially an arbitrary amount of almost any PD in the game, and when you need a heavier raider for the price of the rainbow armor you can instead toss in a MR amulet and either a lucky pendant or bracers of defense (very nice with an E9 bless).

If you're planning on fielding a lot of Sidhe Lord raiders (and why wouldn't you?) E9 helps pays good dividends the whole game. Not to say there isn't an opportunity cost, as it is an expensive investment, just took issue with the claim that it's mostly wasted.