Before reading this post, please note that I am not involved in B1 or B52 operations. The opinions expressed are based entirely on knowledge of military aircraft operations in general. Thank you for listening.
Low level... Hmm...
The definition of low level is, "You and you aircraft are airborne and not touching the ground." 1000 feet is not low level. 500 feet is kind of low level. 50 feet AGL and below IS
low level. An aircraft can fly anywhere between the ground and its operational ceiling. Therefore, the airforce does and has to
practice operations in all permutations of the flight envelope. If it doesn't then it is not maximising the potential of the fleet. More to the point, if it doesn't and the threat changes, then it will be unpreparared to meet the new challenge. And that is the purpose of an airforce (and any other force) that may have to go to war: to be prepared for it if and when it happens.
The definition of a 'Pessimist': an Optimist with experience...