You're desperately trying to get into my sig
The anvil is great. It grants extra dispeldice and extra tracitcal possibilities relating to movement, and wiping skirmishers off the field in spades.
However, it would be a lot greater if it were more reliable, that is its achilles heel. While activating on a 2+ seems great, if you happen to roll that 1, your plans may be ^&%'ed and/or your units stranded. The odds are good enough for the rune to be struck properly, but because it is so enormously vital that they are, it is all the more disastrous if it isn't, and a 1 in 6 chance of disaster happening is not the style of play many dwarfplayers enjoy. Being able to go 'boom' when misstriking is nearly a secondary issue compared to the problem the unit you just set up and left out there to dry has. There is too much importance attached to the failure of he anvil's strike.
On top of that it can be automatically killed (generally granting about 450pts for the runelord & anvil, and another 100 VPs for the general) by initiative tests. With shadow being one of the more popular lores, it will probably experience mass pitting quite rapidly.
The anvil definately has lots of possibilities, but the failing of the roll has far too great downsides and it is easy to destroy with initiative tests. If the failing of the 2+ roll might not entail the possibility of explosions or a turn of uselessnes, you might see it a bit more. For its importance it is not reliable enough in the army renowned for rerolling misfires, artillery dice and scatter dice.