I'd go for the secondhand Fuji, but, knowing what I do, I'd also consider selling your DA35/2.4 and buying a DA35/2.8 macro limited to replace it. That way, you'll get a lens that's lighter than the FA31/1.8, but almost as well built and offers very close focussing, while giving you very good general IQ, in spite of giving away around a stop-and-a-half to the FA31/1.8. I have both the FA31/1.8 and the DA35/2.8 macro limited, by the way.
Given that the X100s is going new here for less than $1,000US, I imagine you'd pick up a secondhand one for around $800US in good condition, leaving you not terribly much out of pocket on top of your windfall, with a better 35 than you have now. I hope that doesn't add too much more pressure on your decision-making.
Last edited by RobA_Oz; 04-22-2014 at 11:36 PM.