Burnout is still an issue even if playing Tests alone. Bowlers will still risk injury in things like back to back Tests, or taking on 50+ overs a match like Murali. Like I said, it's about the recovery time, a sort of "Goldilocks" principle. Bowlers burn out if they don't get any time off, but lose fitness due to long layoffs. Somewhere in the middle is a sustainable work rate.
angryangy added 3 Minutes and 4 Seconds later...
Australia's top order however needs to improve or be changed. On form, Australia has the best middle order (albeit not as violent as those of South Africa or Pakistan), but the top order is behind Sri Lanka, South Africa, England and India.
It's not just about backups such as Paine. Haddin himself gets in and gets out. Ponting can look good when he gets a start, but is facing a struggle to get those starts. Watson has been somewhat consistent, but is equally consistent in playing a poor shot across the line and it denies him the chance to make big scores, or even so much as bat past 20 overs.
For Australia to make a serious attack on the World Cup, at least one permanent change must be made: Clarke must bat in the top order. For those who bemoan his strike rate, do not fret! In the last two years, he has scored much quicker in top order appearances than in the middle order and not just by filling his boots against mediocre sides; he has done best against the top five opponents. Clarke has the form to match players like Amla. Australia might be able to wing it and get away with a collapse in games where such players aren't effective, but when they are, it is going to be necessary to have a good start.