Just a fyi, there isn't a "main singleplayer component" in the sense of a campaign or a set of maps to beat. There is only skirmish.
TEC is probably the easiest to learn, as they require the least micromanagement, and have both the easiest economy to get rolling, and the best economy overall.
As far as I'm concerned, no, it's not worth it just for single player. Not that the AI isn't reasonably challenging (I've yet to best the Vicious AI, though I've only tried a few times) but because I don't really enjoy fighting AIs. Trying to match something with 40 times my resources isn't my idea of a fun time; I much prefer the mental challenge of fighting human players. Without a campaign, single player doesn't hold a long-term attraction for me - even with one, that attraction would last only as long as the campaign. However, as carbon pointed out, I'm in the minority of Sins players - somehow, they manage to enjoy fighting the computer.
Galciv might be a better choice for single player. I don't know if it includes a campaign, but I played the demo a bit and got the feeling it's somewhat like Sid Mier's Civ series, only in space. That is, turn based, much more interesting diplomacy, deeper research, etc - in a phrase, designed for singleplayer. I don't believe there's a multiplayer component at all.