My litmus test for individual-to-individual mentorship might be relevant here:
I am mentoring iff my prospective mentee believes I have helped them grow in ways they wouldn't have achieved as well alone.
Concentrating on the mentee's perspective helps me remember that the value proposition is in what the mentee believes. Of course this isn't perfect, both false negatives and false positives are still possible. I do try to help mentees realistically appreciate their areas of growth (and non-growth), however. I the concentration on growth also helps me distinguish long-term, individualized relationships from (still very valuable) cooperition and general helpfulness.