The main thing putting me off is logistics - organising end point drop-offs and pickups is too hard, and the accommodation options along the way are not really my cup of tea.
It could be the horse thing I guess. The Kidman is billed as a horse/cycle/walking trail, and I think it's mainly set up for horses. Horses seem to need these big float contraptions to carry them round, and this seems to go along with 4WDs and flat areas for parking and all that sort of stuff. Visit Kuitpo forest on a Sunday and it's horse central.
As I said before, Roehr Rd north of Nuri is really nice - but that’s where I double flatted and my pump broke, so took a shortcut back to Tanunda rather than loop round on the Kidman to Pewsey Vale Peak. In any case, the Mawson’s climb on dirt up Trial Hill Rd is really nice, with a great view from the Steingarten vineyard.
There are a couple of sections after Dawsley that can't be ridden. There's a lovely creek crossing (Mt Barker Creek, full of water on the day I was there), and pushing a bike through that is a pleasure, but after that there are a couple of stretches that had become overgrown with prickle bushes, and which were almost impassable. (On Glen Brae Rd after Daniel Rd I think) Certainly not fun, with bikes dragged and legs full of itchy prickles.
Kuitpo forest? Hmm - more pine plantation. Good for horses, and no cars, but it just doesn’t do it for me. After that Adam Gully and Thomas Hill Rd are nice, But really it’s just a dirt trickle into Willunga.
Bonus is if you want to get back to town you can rail-trail it to Seaford and get the train.