It's still a BIG chunk of XP, no matter what, especially if you have an XP boost going and are wearing your XP boosting armor.
If you have THAT many data crystals, you're basically going to be wasting them spending them on anything other than Alliance Crates. Unlock the Priority Transport to Odessan skill under the Legacy Tab (Requires Legacy 5, lvl 55, and 200k credits), use it to go to Odessan, then look for the Smuggled Goods Vendor. She sells Tier 6 Influence items for companions but she also sells Legacy Bound crates of goods. They are 50 a pop, so only buy as many as you need to keep yourself a healthy bit under 1k Data Crystals (the limit) until you hit 65. Once you hit level 65, use your data crystals to buy your Outlander set pieces, making sure to see if you can afford any Exarch pieces first (they use the uncommon data crystals).
You can't DO anything with these until you hit Chapter 9 of Fallen Empire, but the rewards are decent the moment you can use them: a box with a piece of Legacy Armor (5 sets a class, 7 pieces a set) and ether a tier 5/6 Influence item for a companion, a decoration for your Stronghold/house, or a mount, and rep with whoever the crate was for (Ether Military, Science, Force-Users, or Smugglers).
The reason to raise your rep with your alliance is because getting it to 10 unlocks things that can help you do the heroics associated with your Alliance. It's also believed that it will have an effect on the story of Eternal Throne at some point.