From a mechanics perspective. Because you have loose spokes and a wobble I would recommend bringing it in. You have two options. First, they can tighten the loose spokes and true it up (little $$) or, secondly, you can have them loosen all of the spokes and re-tension the wheel (more $$). Without seeing it I cant say which is best.

When do I true (align, straighten) my rims? All the time. I'm a little anal about it so I'm constantly checking and touching them up. A good rule of thumb is to adjust your brakes so theres about the space of a nickel between the brakes and the rim. when your rim rubs the brakes its time to do something.

Regardless of having disk brakes you should have it adressed. If your off-roading it with loose spokes the possibilty of taco-ing (collapsing) your will is greatly increased. That wobble may cause your entire bike to wobble if you go a hill really fast. FWIW I hit 40 MPH going downhill on my MTB a few weeks ago.