I used to wonder if I could still call myself polyamorous if I was dating one or zero people. Answer: yes, because polyamory is about how I do ALL of my relationships, not just about what set of rules I put on my romantic relationships.
For me, polyamory is not about what I DO want so much as it is about what I DON'T want. I don't want to have to put people in roles or privilege my sexual relationship over my friendships in order to make one person feel loved and safe. I don't want to have to limit all my connections so that they don't accidentally develop romantic aspects. I don't want to have to define some cuddles as platonic and others as romantic. I don't want to spend so much time and energy on one person that I cannot imagine my life without them and my identity becomes intermingled with our relationship, thus making it impossible to really know if I even want to be in it, or to know who I am without their influence. I don't want them to get that dependent on me either. I want to feel like my connections to others can be changed at any point by either person without anyone suffering damage (pain maybe, but not damage).
For me, polyamory is not about having multiple partners, it's about refusing artificial limits. My polyamory is practiced just as much when I am single or dating one person. It's easier and more fun when I am dating more than one person! but it isn't any less of a part of who I am.