I see. Still, if I chose to expend the effort, could I use the rules from SM:P to create an entirely new campaign setting, or is the setting too ingrained in the game? I can create a whole new set of races if necessary, I just want to know which system will end up being more flexible and playable for a game master who likes to world-build.
It would be easy to use any edition of Spacemaster in a homebrew setting. The main difference between SPAM and SM1/2 is the level of detail regarding skills. Both SM1 and 2 are detailed regarding skills, as they share the same engine with RM1/2, which currently powers RMC and RMX. However, SPAM shares rules with RMSS/RMFRP, in which there are hundred of skills divided in dozen of categories, and you have to track them all, as points brought in the categories will help individual skills and so on. If you like details, SM1/2 is perhaps you game. If you're thrilled with the idea of several pages long character sheet to bookkeep your skills, then I would recommend you to go with SPAM.
Despite all my negativeness toward the skill rules, there are several small points in which SPAM did better, including armour categories and profession bonuses. If you know the system pretty well, you can probably borrow those things from SPAM to SM2 without much trouble. In fact, many options were ported from RMSS/FRP to RMC.
Both editions are available as pdf files, although only SPAM is currently in print. However, it is fairly easy to get an old copy of SM2 at e-Bay or online game sellers.