I finally got fbvncserver working on my c3100. I had the package on my machine, but not installed, for years. I don't remember if I ever tried it or if it ever worked before. But it didn't work this time. After fiddling around I finally got it to work, for the most part. Here are my steps in case anyone else ever tries it and has the same issues.
Getting fbvncserver-c3000_0.9.4-0.2_arm.ipk working on the C3100
Install the package.
Then, as root:
1) "ln -sf /usr/local/bin/fbvncinput /etc/rc.d/init.d/fbvncinput"
because the link from the package is broken (note: if you start this service without rebooting you will be able to start a vnc server and connect to it but you will not be able to send input to the vnc server. Do not run it.)
2) edit all "vncserver_*" files under /usr/local/bin/ and remove the "-r0" from their vnc server launch commands (last line). That option causes vncserver to segfault for some reason. I suspect it is a screen rotation command (0 meaning no rotation) but I was unable to find any info on that command on the web.
3) reboot and then do the screen calibration by taping the very top left and then the very bottom right (including the quick icon area). If you check your running processes you should now have a "tssimd" service running and the kernel module "kbdsim" loaded. If not, then something is still not working.
4) launch the server utility and choose double or normal. I don't think the rotate one works and for me both choices launch a double size server. Oh well. But at least it works now on the c3100 and probably the c3200 as well.