Think of the energy and building material that would give. All we'd need is for the molten magma stream to boil some water on the way out, and while still molten, be transported to the site of whatever massive construction project we choose. Maybe tie the two together, using some fancy Leidenfrost effect to keep the hot lava flowing on a cushion of steam. Once the lava gets to its destination, huge bots with chilled trowels would form it into walls or sculptures. With enough magma to fill the grand canyon, we could build an urban area big enough to cover most of Wyoming. Make the buildings free to homesteaders who agree to bring the buildings up to code. Name it 'Magma, Wyoming' or something. Also do a monument like Rushmore, but featuring all the presidents. Make each head the size of a mountain and call the new range The Presidentials. See? Lemons into lemonade.