One question - is there a way to use inotify without the need to provide the root password for mounting/umounting?
Use of inotify has no impact on mounting/unmounting, it is only used to detect changes in directory contents, and has nothing to do with root passwords.
If you are using the default udisks build (built without --enable-hal), then I don't see how you can be getting any prompt for a root password when clicking Mount or Unmount, unless you are explicitly selecting Root > Unmount from the devices context menu. Do you mean you are getting an error 'Only root can unmount...'? If so, then udisks may not be properly authorized - usually a system configuration problem.
You can test this by opening a terminal and using udisks directly to mount/unmount the device (replace 'sdX' with the correct device file):
udisks --mount /dev/sdX
udisks --unmount /dev/sdX
If you are able to do that without errors, then generally spacefm will be able to as well - it uses those same commands. If you receive an error, then it is usually due to options in fstab preventing the device from being mounted as a user ('Error only root can unmount...', or udisks is not authorized through consolekit/policykit ('Not Authorized') - a system config issue.
You can also participate in this thread
to help clarify what is happening. There is simply no code to ask for a root password during normal user mount/unmount (in the udisks build) - if root is required then you'll just get an error. So first we need to clarify exactly what you're doing and what response you're getting. Thanks.