This is fairly literal, apart from "support" for "consenso", which I admit is fairly free. You could stay closer by using something like "the level of consensus it has achieved/created" (not just "its level of consensus", I think; that wouldn't quite work). It would sound OK, but would be less clear, I think. I suppose the idea of "consenso", strictly speaking, is getting people to agree with each other. But in practice, as the contextual explanation shows, what it's really referring to is the party's percentage support in polls, and I think "level of support" would convey the right idea in a more natural way. I don't see any need to use "levels", in the plural, literally matching the Spanish; I don't think it makes any difference to the meaning, and the singular seems more natural to me.

"Reap the benefits", for rentabilizar, refers to the fact that in to the Spanish system small parties are disadvantaged by the threshold for parliamentary representation, which doesn't match their percentage of the popular vote if this is below about 10%. They have not succeeded in breaking through to the point that they reap the benefits by gaining a number of seats in parliament to match their percentage support from voters. The same is true, in a different way, in the UK's "first past the post" system.

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Note added at 3 hrs (2015-01-15 03:01:32 GMT)
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I'm pretty sure "consenso" is referring to a consensus among voters rather than among parties. Actually, as Andy says, the latter has not happened: Ciudadanos has not managed to agree a pact with UPyD, and an agreement with Podemos does not seem to be on the cards. Nevertheless, it might be a good idea to use my more literal alternative, "the level of consensus it has achieved". Ciudadanos does talk about "consenso" quite a lot.