Since I wanted a lot of things to be weighted when determining the search order, I considered just hiding all the complexity 'under the hood'.

The way I view it, search rankings are a tool like any other. In my own experience in academic research I've always found that clearly defined search rankings are more useful to me than generic rankings; if you know how the tool works, it's easier to use correctly. That said, there's probably still a place for a complex algorithm alongside other search tools, it just shouldn't be the only search tool.

But if people don't know what they are voting on they might be less inclined to vote at all.

Well I think it's more a matter of efficiently extracting information from users. Consider the LessWrong karma system, while it serves its purpose of filtering out spam, its a very noisy indicator of anything other than 'people thought this comment should get karma'. This is because some users think that we should vote things up or down based on different criteria, such as: do I agree with this comment?; did this comment contain valuable information for me?; was this an amusing comment?; was this comment well reasoned?; and so on.

By clearly defining the voting criteria, you're not just making users more likely to vote, you're also more efficiently extracting information out of them. From a user perspective this can be really useful, knowing that a particular rating is the popularity or the importance of a project, they can then choose whether they want to pay attention to or ignore that metric.