I am pretty sure newer is not always better. I've learned it with the D700
never replaced it for more than 3 years until I got the E-M5. I only got the E-M5 coz I want a smaller camera.
The only reason I did not replace the D700 was because I was so satisfied with it I never even considered nor lust for other cameras. Now since the OP is asking/thinking about the x100s I assume he is interested about it since he's willing to spend more to get it. From my personal view, it's almost futile to fight the urge.
hehe
Otherwise any current camera can get you decent results IQ wise. I chose the X-E1 coz I want a system camera, I don't expect it to have better IQ than the E-M5/E-P5, I just expect it to be different and boy is it different. haha I like!!