The only reason I'd need it is getting rid of old anvils. Even with 0 resources returned
Oherwise - game needs a reason to play. Gathering new resources is one of that.
By providing means to get your resources back you reduce time to gather new resources.
First I've wrote a detailed description about new recycler(smelter) satructure and how it should work. But after writing this I've found out that its to much dev work for too little game content. There are lots of better things to invest time.
So -1 for all cases except easy way do destroy anvils =)