If your experiance is limited to wood glue and dowels, then you really don't have much to say about the real possiblities of using alternative materials. Using wood glue and dowels on a wooden frame member would be like trying to solder your axel back together. You can't simply weld all types of metal back together again either. Welding of cast metal parts isn't recommended, so usualy you recycle the old part and buy a new one. In addition, common welding as we know it now has serious effects on the temper of the parts being joined. Repared metal isn't an ideal material either. If it were, you wouldn't need car fax.
Wood can be bonded very strongly. I don't know about any one else, but I don't plan on driving my car, truck, or tractor nto a furnace, or intentionally scraping the frame with abrasives. Incredable things can be acomplished using the apropriate wood in places you wouldn't normally think of. There are woods that are extremely abrasion resistant. Old timers made equipment much stronger than most things you can get your hands on now using wood. Of course they weren't dumb enough to not use other materials where apropriate. They also were able to understand and use wood for the purposes you are saying are not ideal, and got better results than using metal alone. Just read about the planes earlier in this thread. Why are some of the best luxury cars built with wood frame members? Did you ever think that some composite materials use wood as a base material?