Well I think it would spread some money around a little better to be honest.To be fair though, why bother with that?
The trouble is, basing CL places on league positions leads to the staleness of the top 4 brigade that we've had for years now (until this season). Top top teams come fourth, they scoop all the money from CL TV rights, and use it to set about securing their CL spot for next season, where the cycle repeats.
The element of randomness inherent in one-leg knockout tournaments like the FA Cup would make it much more open and exciting, and hopefully spread the cash around the league a bit more. Over the last ten years, the likes of Southampton, Everton, Portsmouth and even Millwall could have had a bit of the money that usually just flows straight into Arsenal/Man Utd/Chelsea/Liverpool's pockets.
And it would only be one place, hardly like we're devaluing a competition that gives us four spots anyway.