R/W Expertise

Expertise reduces the energy costs of attack skills, preparations, and traps.

Does this extend to Warrior attack skills? Or does this only work for Ranger attack skills.

I was thinking that a Ranger that could constantly spam out a stream of Warrior attacks wouldn't be too bad off even with the lack of helm and runes.

It applies to warrior attacks skills as well.

IIRC, Expertise does indeed reduce the cost of Warrior Skills and Stances; something to consider though, some of the best Warrior Skills are Adrenal Based (not affected by Expertise, I'm pretty sure) and some of the offensive Energy based skills like Power Attack and Griffin's Sweep and nice stances like Beserker's Stance are connected to the Strength Attribute and since you can't really increase the damage or time length of these skills since you're a Ranger Primary, you'll probably lose out on these skills.

hammer mastery has some energy-using skills of note.

The Beast Mastery stance is much better than Berserker's Stance. With a high beast mastery you can keep it going nonstop, and also you can use attack skills out of it.