money and time has been spent unnecessarily on converting already outstanding and good schools in areas with perfectly good LAs into academies
The DfE pays up to £25,000 to each school that converts. Any additional conversion costs must be met by the school itself. The argument for doing this is that by freeing the school from LA control it will be able to perform better than would be the case if it remained in LA control.
not enough money and time has been spent on dealing with schools not in special measures but not performing as well as could be expected??? Why?
If a school is not in special measures the DfE can only intervene if the LA issues a warning notice. Whilst the Secretary of State has the power to force the LA to consider giving a warning notice and, if the LA refuses, to direct them to do so. This takes time, can be resisted by the LA (who can, of course, go to judicial review, thereby delaying the process by several months) and can be politically difficult. The LA and local campaigners will almost always claim the direction is politically motivated and that there is nothing wrong with the school.
why would an LA object to a failing school becoming an academy and what basis would they be able to fight it in the case of a consistently failing school
They object because they are ideologically opposed to academies. There are usually claims that the forced conversion is politically motivated, that the school can't be expected to do any better (the argument being that children from deprived backgrounds can't possibly be expected to achieve good results at school), that it has already improved and so on.
I thought the legal challenges were mounted in relation to schools which had already shown marked improvements and had credible improvement plans in place
That was usually claimed. That does not necessarily mean those claims were true. When a school has been below floor standard for years claims that it has suddenly improved when faced with forced conversion to academy status are difficult to believe.
Are schools which have been forced to convert required to improve as quickly as schools under threat of academisation
A school that converts to academy status will be given a bit of breathing space to sort out the new arrangements but it will normally get a Section 8 (monitoring) inspection within 2 terms. If there are serious concerns this will be deemed to be a Section 5 (full) inspection and the school will be treated like any other failing school. If progress is inadequate but not poor enough to raise serious concerns the school will be given priorities for improvement and will be assessed again with a Section 5 inspection early in the second year of operation (typically the fourth term after opening).