If your server is anything like mine, nexus crystals are worth nearly nothing. I can pick them up for under 1 g each on the AH. Whenever I purchase these. I turn them into small prismatic shards via Nexus Transformation. From there I usually turn them into large prismatic shards where I can sell them for between 8-15g depending on the market.
Its not a large profit margin, but a small gimmick that you can queue your self to process while you open up your mailbox.