Dex damage appeals to me. Just 1d2/1d2 perhaps, or 1d3/1d2 (midway between 1/2 HD Tiny monstrous spiders and 1 HD Small monstrous spiders)?
I think those are ok. Let's do dazzled for Y=1d4 rounds on a failed save. I can wait to see how the rest looks before deciding on the racial bonus. For dust form, instead of saying "but it can not move, attack or take any action (including spellcasting) which has a verbal, somatic or material component" why not say "but can take only purely mental actions"?
Cannot move, but can reform as a move action? I get it, but it has the potential to be confusing. There has to be a better way of phrasing.
For the dustform, perhaps one of these more simplistic solutions can be adapted...
Unravel (Ex): Once per day as a standard action, a hangman golem can unravel its form to become a heap of tangled ropes that fills a 10-foot-by-10-foot area. While in this form, the rope golem cannot attack or move, but it gains fast healing 10. A hangman golem can reform into its humanoid appearance as a full-round action.
Boulder Defense (Ex): A thomil can change its shape to a smooth, immobile, boulderlike form. In this form, the thomil's damage reduction increases to 15/- and its spell resistance increases by 5, but it cannot move or make attacks. Assuming this form takes a standard action, while returning to its semihumanoid form is a free action.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.