Pluses and minuses to everything... Something like a FLIR Breach is a great tool for spotting animals at night. It's relatively affordable, can be easily head mounted, small, light etc.. That's what I run for spotting. It's not the only answer, though.
On the weapon I go back and forth. You can often see things with the Breach that you can't see with NV because of illuminator bloom, shadows, foliage, etc... In those instances I wished I had a thermal on the gun, too. I have also, however, called in foxes while calling coyotes and couldn't see the difference in the thermal. I thought I was dealing with a coyote until I found him in the NV. I think with a good thermal unit on the rifle and some experience watching animals with it a guy could probably be okay running just thermal... Except on nights where it's wet/misty/humid where everything is the same temp.. Makes navigation very challenging.
My current set up is a PVS14 + Breach helmet mount. Weapon has an IR laser (fast movers <50m) and I just got in my Super Yoter R for longer shots. I'm anxious to get out this winter and put that Yoter through its paces. So far very impressed with it.