I think this role is absolutely essential.
It will provide the means to ensure that experienced social workers don't have to abandon their skills in the field and pursue a management career, simply to be able to gain a suitable salary.
The role would be particularly suitable for the big towns and cities where the high cost of living encourages experienced social workers to give up their roles, simply to be able to pay a mortgage. Although social work is a vocational undertaking, it isn't a profession that should by default be seen as low paid.
Advanced social workers will be key in mentoring junior staff, arbitrating in difficult decisions and, but only if their role is correctly defined, ensuring that the decisions made by management are fully appreciated for what impact they will have in reality in the field.
The concern would be that some managers will be unable to cope with advanced social workers, fearful of their status and salary. The only useful positive analogy I can make is that in the Army (not just the British Army) it isn't unusual to find experienced NCO's - Non-Commissioned Officers, such a Regimental or Master Sergeants, who earn more than junior officers. Since before the Vietnam War the US Army's master sergeants are invariably on a higher salary than platoon second lieutenants (source: We Were Soldiers Once...and Young - Lieutenant General Hal Moore and Joseph L Galloway.) Obviously we don't want to associate social work with military practises, but the concept that experienced workers are recognised for their worth, to the point that they invariably earn more than their "junior" managers is an established and useful one.
For the likes of Inner London I would like to see the role of advanced social worker subject to a pay scale that tops out at 90k. For that salary I would expect to see the submission of academic papers, a proper degree and nigh-on god-like reverence amongst their peers. Certainly with the introduction of advanced social workers I would expect to see the incidences of well-publicised blunders like the Fran Lyon scandal become a thing of the past. We would expect senior social workers to impose and maintain high standards of professionalism, so that we don't hear of critisisms such as pooor grammar and spelling being applied to documentation, or junior staff being unable to cope when they are asked a simple question in a Family Court session. The idea is that the link between management and staff, which can be teneous at best and downright abusive at worst, is transformed.