Nah I've worked on the 6G72 (Mitsu engine in the Stealth) a few times, engine doesn't need to come out, but the intake manifold and some other crap needs to be pulled off to get to the rear bank of plugs. On my Grand Prix I have to disconnect the upper engine mounts and rock the engine forward, then literally laying on top the engine reach back and get at the rear plugs by feel. Takes me literally 5 minutes to change the front plugs and I've had the rears take almost 2 hours. It sucks.
Yeah on Subaru's the plugs are a bitch to reach. Try getting to the O2 sensor on that engine some time, real good time lol. I like Subies quite a lot, but the thought of replacing anything on those boxer engines sends chills up my spine.