I have a PodXT Live and an X3Live. I never really got around to tweaking the X3 as much as I did the first one. To me, the XT sounded great, and was all I needed.
So what we're dealing with is simple nostalgia, and perhaps familariarty with a device. I think I'll be able to do with the 500x what I was able to do with the XT, albeit with different routes to achiving a desired tone. After all, it just simulates the routing of effects and position of mic, they're numbers, it's a program, nothing is physically there and those values only serve as a reference for what you're attempting to achive. If I got a solid metal tone with my computerized mic upside down, behind the amp, and under water, those would be the settings I'd choose. I think many people forget that.