Finchy, that's a brave question here - some people can be very touchy about what they consider should be "done" and are quick to suggest that those who disagree are somehow being cruel - I hope you have a thick hide

. Yet somehow separating the genders of Gouldians is considered "good" coz it gets the males raring to go

(even though there is no evidence of cloistering in the wild).
Zebs are colony birds quite apart from being prolific breeders. A few males together sans females gives them some one to play with even if not someone to "play" with

. I knew a guy once (lost touch with him over the years) who kept his pets and his breeding stock quite happily apart with never an ill effect on the birds. He had dozens of "misfits" in relation to show standard he would never intend to breed from but whose appearance caught his fancy. These were kept in separate male and female flights and all lived out their days without suffering any depression that I saw.