I've cooked with tempeh, tofu, wheat gluten, and many other soy products. Some people think of these as meat substitutes but in the cuisines in which they originated, they are just food (protein-rich food in particular; they're not meant to replicate meat. I use the word meat substitute, on the other hand, to refer to commercial food products that actually replicate meat, such as "veggie steak strips," and "veggie chik'n patties." I've cooked with these as well, but as you say, they're nothing like meat (in most cases) and can't be cooked just like meat. The biggest thing missing is collagen, which melts as meat cooks and enriches its texture and juiciness. That's one of the primary difference between plant foods and animal foods: fat and particularly collagen. You can't braise a piece of tofu and expect it to release collagen into the braising liquid as a beef chuck roast would for example, enriching the mouthfeel of the liquid with a tongue-coating unctuousness.
Sometimes when cooking with soy products, I add quite a bit of fat to improve mouthfeel. Sesame oil, nut butters (cashew is excellent), sesame butter (tahini), and other fatty plant foods (cocounut milk) help to improve mouthfeel in sauces and other preparations for soy foods.
For instance, have you ever had the classic Indian dish Navrattan Korma (vegetables in a rich nut butter sauce)? When cubes of tofu and/or vegetables are simmered in this rich sauce, the fat in the sauce improves the mouthfeel of the tofu. I also like to twice-cook tofu. I typically brown tofu to cook off excess moisture and crisp the surface, then braise it, marinate it, grill it, etc to add flavor and a sauce.
As you mentioned, the long drawn-out cooking techniques used for meat, such as barbecuing, typically don't work well with vegetables. These long-cooking methods were developed to soften the tough fibers in muscle (meat) so that the food is palatable. Such cooking isn't necessary with most vegetables and will break down the fibers so much that the food ends up tasting mushy. However, some vegetables do braise well, especially those with relatively tough fibers, such as potatoes, leeks (and other alliums), fennel, and cabbage. | 
