If you intend to keep your XD-E, it makes sense to buy a recoil spring and hang on to it. A pistol should shoot 5,000 rounds or so on a spring... but it would be good to have an extra. Other springs (hammer, trigger return, etc.) should last forever. But in the unlikely event they fail, you can probably find something out there that would work - perhaps consulting with Springfield or Wolff or somebody who has a supply of different springs on hand.
I don't see the supply of "wear parts" as being a serious problem. I have a Colt 1903 .32 ACP that's been in the family since it was made in the mid-1920's, and it has all original parts and springs - except I did replace the recoil spring with a Wolff when it was handed down to me a couple of years ago. If a major part breaks on your XD-E -- well, Springfield will have them on hand for a while, and then you are kinda on your own. As the years go by, the price of a used XD-E will probably drop. It may be plausible to buy a used one in a year or two -- just for the parts.
Magazines are a different issue. If you want a few extras -- might be a good idea to get one or two now.