The lava ingots can be used for all sorts of recipes in other mods, providing a great use for lava; as noted, stuff dug with lava tools is put in your inventory as the smelted item (digging cobble, for example, yields stone), and lava tools can light players/nodes on fire (seems a little OP, but definitely realistic :)), so the tools actually serve a purpose!
I have experimented with setups to farm lava ingots the fastest and have settled on one that uses pipeworks: 4 advanced vacuuming tube segments with max range (8) are put on the sides of an autocrafter which is configured to craft lava orbs and is sitting in a lava lake. You will only need to fill the autocrafter with maybe a few stacks of mese crystals, and then fill your inventory with random items. The trick is to have your inventory full, so the buckets drop after collecting the lava, which are then vacuumed and processed by the autocrafter. The empty buckets are then found in the output slots of the autocrafter, so you can do it over again. After you've gathered all the lava you can in that spot, you can move to a new lava lake.