Light rail service to Maricopa? I just can't see it. Maricopa is way beyond what I'd consider a reasonable extension of Valley Metro light rail service. Given that there isn't even local bus service in Maricopa (as best I can tell), the recently-started Thruway connection between Maricopa - Tempe - Phoenix is probably going to have to suffice.
Palm Springs? California has been studying additional rail service from Los Angeles to the Coachella Valley. Most recently the thought had been 2 Amtrak roundtrips/day, but the cost numbers were, uh, not promising.