In fact, the whole reason he horned in on the theme music, so the story goes, was as a hedge against the show's failure. He didn't expect to make any profit from the show itself (or at least was cautious enough to prepare for the possibility that he wouldn't), so he added lyrics to the theme so that he could at least make a few bucks from sheet music sales -- which, if the show had bombed, would've been his only real hope of seeing any profit from it.
At a certain point, Roddenberry's claim that he wasn't going to make any money from Star Trek
doesn't hold water. As the show's producer during the first broadcast season (1966-67), he was paid $3,000 per episode and had an annual guarantee of at least $85,000. That doesn't include his payment for writing or re-writing scripts.
It's reasonable to assume that Roddenberry was worried about his bottom line before the series was picked up, which happened in February of 1966, but isn't the income from sheet music sales pretty much zero when the music is for a television series nobody has seen (i.e. a failed pilot)?
In other words, if the show wasn't picked up, the value of half the music royalties for the theme would be almost nothing. If it was picked up, Roddenberry's income was such that he was making a sizeable income from Star Trek
. (Adjusted for inflation, his guaranteed salary alone would be almost $600,000 in 2012 dollars).
You have to give the man credit, though. Given the show's success in syndication, Roddenberry's share of the theme music royalties must have been pretty helpful financially during the comparatively lean seventies.