The chmod will work but presents lots of problems... allowing everyone to modify the file, if udev is used the chmod won't survive a reboot, and some programs might freak out by seeing odd permissions (like SELinux audit daemons or something similar).
The standard response is to give your user account sudo privileges to run the command. Though, that kind of modification might be ticky to articulate in the sudoers file.
The reason your script does not work is because Linux does not recognize the setuid bit on scripts (assuming you meant setuid instead of sudo).
However, you might be able to combine the two approaches. If the script works as you want, give your user sudo permission to run the script as root. That would be easier than writing a sudoers rule to let the user echo specific values to a /proc/scsi/scsi. I'm guessing the rule would look something like this:
username ALL = (root) NOPASSWD: /path/to/script.bash
And would be used like this:
sudo -u root /path/to/script.bash arg1 arg2 ...
Disclaimer: I'm a relative novice using sudo. So I make no guarantees the solution above will work "out of the box."