Currently, items enchant values that are equivalent to the item's level. However, there's a major change coming in the next build, and this thread was the most appropriate to communicate it in given the topic at hand.
In the next Beta patch, Legacy items (or items that drop prior to Patch 2.0.1) will no longer be able to be enchanted. This was a decision we ultimately made because certain Legacy items, when enchanted, became disproportionately strong compared to new items, which isn't the intent.
However, there's an interesting "bug," if you'd like to call it, that will result from this change in the next Beta patch - all items gained up until the patch will no longer be able to be enchanted. This is an artifact of the fix implementation, and we felt it prudent to communicate this as soon as we could for those of you in the Beta. All items that drop in Patch 2.0.1 and forward will be able to be enchanted, so this shouldn't be an issue as we move into the live patch and onward to the expansion launch.
*Edited in some additional clarification*
Edited by Nevalistis on 2/4/2014 8:13 PM PST