Please take the time to get to at least solo standard in gliders as well. There is little worse than a time builder on the front of the rope who has no real interest in what is going on at the other end. As a CASA Tow Pilot training delegate, (and Level 2 Gliding Instructor) I have had several sub-optimal experiences over the years training Commercial pilots to tow gliders who really only saw it as a cheap way to build hours.
The GFA Manual of Standard Procedures recommends that tow pilots be glider pilots as well.
If you fly gliders, you will understand what the glider pilot is looking for, regards what part of the sky to take her/him to. Remember it is the glider pilot who is paying for the operation. As already said by others, glider flying will certainly improve your hands on skills in other forms of aviation. Not to mention all those take offs and landings in the tug.
Many ATPL guys & Pruners fly gliders for fun and the current Chief of the Air Force started his aviation carrier in gliders all those years ago and owns and flys his own glider even now.
It really is great fun flying tugs. You will have a ball!
Greeb