Please do update the robots.txt file 
I do link to mine e.g. on this very forum because it can be instructive.
So unless you plan to privatise this forum (which I also believe would be prudent), you should update robots.txt so people can make their sandbox a more collaborative tool.
In both cases, I think you’ll see uptick in usage if you give people more privacy on those fronts.
Privacy concerns are rarely acute enough for users to surface, but they act like a sludge on user behavior.