Expanding is necessary, otherwise you will lose on Victory Points. The game does not lend itself to turtling. I realize that is not really your question though.

The strategies have not really been fleshed out right now. The seed/nexus is very strong, so it will be effectively impossible to win with a rush snipe tactic. But rushing may still be effective for hurting your opponent's econ in the early game, depending upon map size (even the small maps take a fair amount of time to traverse). As for rush vs. boom, I think the trade off works because, though you still need to expand, you need to put extractors on the various resource points to pull in more faster, and building them takes away resources for units. Radioactives, needed to build advanced units, are also needed to build Quanta complexes (or whatever they are called) for research and global abilities. I think there are a continuum of workable strategies, though the differences in this game are subtle because expansion is necessary either way.