I don't see £20m a season over four years and repeated 6th place finishes as a great achievement. Had it been a couple of 4th places I'd have agreed though. 5th and 6th place are best of the rest positions really.To use the same stats as the OP from the Mail, it looks as though for 2008-09 in isolation the net investment was £40m+. If O'Neill hadn't achieved the holy grail of CL football after that spend then perhaps Lerner felt disinclined to provide any more funds.
How much money could be raised by selling the players that are left? I'd imagine £80million could be recouped easily. Figures can be used both ways.