Crit shields are VERY nice, but unreliable no matter how much CHR you stack. However, if your other healers share gear with your SCH, you are still going to benefit from CHR. I don't play AST, but my WHM has more abilities that can crit compared to SCH. Since I main both, I have always placed CHR above SS when my healers share gear. That said, the only gear they shared through the leveling stages were belt and accessories. I always crafted two sets of each of the remaining slots to customize stats and glamour. This is totally not required for your healers in the leveling stages, and just something I enjoy doing.

For the custom slots (head, body, hands, legs, feet), I would meld SS for my SCH instead of CHR, when I could. If using HQ gear, secondary stats on the item are often at, or near cap. If the piece of gear could not benefit from a SS meld, then it gets CHR by default. If neither could be used, then I used DET. And that is basically it all the way to 60.