Having done an EPQ this year, I can tell you that passion really helps. My topic was so interesting which made me really passionate about it, thus I dedicated far more time to my project than others who also did it. The level of quality I found when looking at others EPQs, was almost correlational to their passion for their chosen subject. This year we had about 60+ interested in doing an EPQ, with only 14 finishing it. Lots of people drop out due to the time commitment of other subjects. If you're planning on applying to Oxbridge, whilst an EPQ may look favourable, I'm sure they'd rather you maintain high standards in your A-Levels. You do get a lot out of the project though, not just the knowledge, but also the skills like time management, independent study ect, which unis value so highly, so I think if you were to do any degree, the EPQ would benefit you in some way.