A few universities actually lower your A-level requirements if you achieve a high grade in the EPQ. I believe both Lancaster and Exeter do this. Many will also take this qualification into consideration where you've narrowly missed your required grades for entry too.
Personally, I found that it was great qualification to do because it didn't take up time in the same way A-levels did (no revision or exams to worry about), it was completely orientated around a subject you could chose, and it still awards UCAS points. I would only recommend it if you're doing 3 A-levels and no AS in your second year though, as five courses could frazzle you!