Unless User:Alicorn is currently using the time saved by not preserving metal for other activities which have the effect of saving more metal (or equivalent paperclip inputs), then there is no relevant opportunity cost to User:Alicorn preserving the aluminum for recycling.
I suspect that Alicorn is currently using the time saved for activities that further her values. Are you using the time saved by not providing Alicorn with incentives to preserve metal to further your values for activities that save more equivalent paperclip inputs?
On Saturday, New Haven residents, people who live in other nearby assorted Havens, and anybody else who would like to trek out here are welcomed to a Less Wrong meetup in thomblake's and my home at noon(ish). The address is thus:
173 Russo Ave Unit 406
East Haven, CT 06513
I will make food; if you plan to come and wish to submit food-related requests, say so.