See my earlier post regarding the 'hi' & 'lo' issue - for 'lo', I've said I believe the OV-10 to be a better solution than A-29 or AT-6, for any number of reasons but not limited to, inherent flexibility with twin - engined resilience.
I don't think anyone, least of all me, is advocating the A-10 as an attack 'panacea', although in a loitering battlefield environment, I can personally think of little, if anything, that's better.
And I'd love to know how 'cheap' those A-29s & AT-6s (along with their crews) would prove when the bad guys shoot back, or the threat changes.