I must be one of the most privileged trainers on the planet! Just look at the view from my saddle today!
I think keeping horses happy in their work is really important. One of my approaches to accomplishing this is by cross training. No matter what discipline a horses training is focus upon, trail rides are so beneficial for the horse. The horse must use different muscle groups for this type of work and certainly the horses balance is improved on, as well. The exposure to a new and changing environment is also stimulating to the horses mind. I think this really helps to keep the horses mind fresh and interested in work.
Currently I can tack-up and trail ride right out of the barn. This certainly makes it simple to add trail riding as part of my cross training. If you must load up and haul to trail ride, I still recommend doing so. The extra added effort will pay off in the long run of keeping your horses mind and body refreshed. It is always best if you can use the buddy system to trail ride. Not only does this provide an amount of back-up, should one of you run into trouble, but multiple horses and humans get out to enjoy the scenery!