I think the process of guessing would have been more enjoyable had there been no leak, but in the grand scheme of things it doesn't really matter. It helped that there were so many curveballs in this expansion, so we could discuss the exciting choices and how they would fit into the game. If the leaked list had been 9 obvious civs and leaders I think it would have felt more of an anticlimax.
The way it worked out just meant we had an initial flurry of new info, rather than a drip feed. But there's been enough information to uncover over the past few weeks in terms of new units and mechanics that we haven't exactly been spoiled by the early leak. Certainly the disappointingly vague "sneak peeks" would have been a lot more frustrating (that's not a good thing) if we didn't have the leak to work from.
In any case, it matters little whether we like it or not—leakers gonna leak. Its up to Firaxis to plug its holes, but I don't think they have lost out either way. Any hype is good hype.