I take a somewhat pragmatic approach. It's unlikely that the ratio of solid scientific knowledge to bogus knowledge is much different today than it was at other points in human history. My basis for the claim comes from reading histories of science and scientists. Invariably, false scientific ideas turn out to be reasonable and potentially correct explanations of the available data. When advancements in instruments, observation technique, and experimentation arise, they tend to make falsified science look wrong. At the time the ideas were proposed, that data didn't exist. There's no reason to think we've reached the limits of observation.
Further, science seems to advance on the backs of creative insights which come from the minds of especially gifted thinkers. (My thinking on this comes from my reading of Thomas Kuhn, especially The Structure of Scientific Revolutions.) Our minds have the remarkable ability to tolerate inconsistent data and we can go a long time accepting mistaken theories before a sudden insight causes us to accept an alternative that better fits the data. The feeling that every bit of new data fits our models is a dangerous bias. We tend to dismiss counter-indicators as "outliers".
Now, we probably do know more in an absolute sense. Given that new knowledge is informed by previous work, we've learned from mistakes and refined theories. Engineering feats that depend on fundamental science validate (from a pragmatic sense) that we know more then we once did. But we also assert many, many more things then we once did. Some things we "know" are based on natural phenomenon that were unknown even a generation ago. (I'm thinking of things like medical claims, computer science theories, and particle physics. There are likely theories that I can't begin to understand in other realms of knowledge.) In order for the ratio of things we know to keep up with the number of things we claim, it's inevitable that we know more in an absolute sense.
A more difficult question is how do we know which claims are true and which claims are bogus. The example of Aristotelean physics suggests that simply picking the most respectable theories isn't a certain way to select true theories.