I agree denotationally with that estimate, but I think you're putting too much emphasis on voting in at least the 0-4 range. Elections (in the US) only come up once or exceptionally twice a year, after all. If you're looking for an estimate of politics' significance to a person's overall life, I think you'd be better off measuring degree of engagement with current events and involvement in political groups -- the latter meaning not only directed activism, but also political blogs, non-activist societies with a partisan slant, and the like.

For example: do you now, or have you ever, owned a political bumper sticker?