Torquelink,
Lets just say I am in a position to know more than most when it comes to how aircraft are valued and why.
Part of the reason behind the devaluation is the low numbers of RR powered vs their GE and PW powered cousins. Aircraft configurations in low numbers have historically been worth less.
Another part of the devaluation is much darker and if one were to search around here they may figure it out. All RR powered 747, 767 operators are very concerned about this problem and will do almost anything to remove themselves from it.
Qantas recently tried to trade in some of their 744s for 777s and were told a resounding "NO". Its getting harder and harder to place aircraft that have this problem.
