Hoo, boy. I'm not really sure how to rate this, but it's got a monster entry so we're gonna try anyway.
To make this a bit more manageable, I'm going to assume that we're talking about a 1 HD psicrystal here (as anything with more is likely to be way less interesting as a PC), who doesn't have a master and is completely free-willed. With those assumptions out of the way, let's go!
What're the abilities of such a psicrystal? A mixed bag. Fine size is a semi-useful niche (only replicated by hairy spiders and Returned-To-Nature Half Giants). Hardness 8 is very powerful.
The real problem here is that going by the rules laid out above (no master), our psicrystal can't benefit from Self-Propulsion. Because of this, it lacks a strength and dexterity score, and doesn't have a movement speed either. This isn't all bad, because at least it can now use intelligence for initiative, but it's hardly good.
Improved Evasion is actually surprisingly useful. While having no dexterity score makes you fail Reflex saves automatically, the ability still reduces their damage by half.
Further limitations of being a little crystal: no limbs, presumably less item slots, and an inability to see beyond 40 ft.
Even worse: the most obvious route (SAD intelligence psion) is complicated greatly by an innate -4 intelligence.
In the end, the resilience and small size of psicrystals don't save them from -0 LA. Not only do they lack basic functions, they also can't really put those defensive abilities to use.
However, when houseruled to have control over abilities that normally require a master, as well as the ability to get advancements as it increases in HD, the psicrystal might be worth +0 or even +1. I'll stick with the relatively safe rating of -0/+0, with the exact value depending on what steps the DM takes to make this playable.