NPR's 2014 news article and audio podcast: Space Thief Or Hero? One Man's Quest To Reawaken An Old Friend quotes Robert Farquhar (NASA, Wikipedia) when discussing the ISEE-3 mission before the ISEE-3 Reboot started:
"It's the most cost-effective spacecraft we ever had and I'd like to make it even more cost-effective. It can do more missions," says Farquhar.
Question: In what ways can it be argued (by Farquhar or others knowledgable on the subject) that ISEE-3 was "the most cost-effective spacecraft we ever had"?