Just to tell a few:Efficiency is only a concern if you make it a concern, and it doesn't require constant input of cobble from an extruder. When you want lava, you put in cobblestone. Cobblestone is pretty easy to get. We're not talking about a magma crucible as part of a power plant. I'm talking about a magma crucible as a means to make lava. Do you know of any uses for lava beyond fuel? I do.
a) it's good for TC3 research
b) automating your smeltery from TiC
c) anything that requires lava in the world
And think outside the box on fuel sources. Jess is powering his entire base solely on a sugar plant, and Saice has an energy-free mass producing cactus coke plant that literally requires no energy, being the most fuel efficient thing I've ever seen.