The big cost in these systems is the water since they're placed in locations where land is cheap (read: otherwise worthless). So conquering the spaces between circles really isn't very important. The key is to increase yield-per-gallon of water not yield-per-acre as is typical with farms.
In yield-per-acre scenarios we already have horizontal irrigation systems that roll across a given area kind of like that giant lane-spanning Chinese bus that recently made the news. The only disadvantage to these systems is they have more moving parts (two sets of wheels) and are limited in how far they can roll (they're usually hooked up to coiling hose systems) so you need more of them.
In yield-per-acre scenarios we already have horizontal irrigation systems that roll across a given area kind of like that giant lane-spanning Chinese bus that recently made the news. The only disadvantage to these systems is they have more moving parts (two sets of wheels) and are limited in how far they can roll (they're usually hooked up to coiling hose systems) so you need more of them.