The skyblock economy revolves around player shops, so the money stays within actual players, but if there was an admin shop, money would be lost and people would just lower their prices to be better than the admin shop.
No support this would take alot of money out of the economy but since there is a problem with spawners and eggs But another idea you could use to get working spawners is make a challenge for each of the eggs and when you get a spawner and that egg and complete the challenge you get a working spawner with the mob in it
I posted this awhile back. It may help articulate why a server shop could be beneficial if used properly. http://www.mineverse.com/threads/skyblock-small-server-shop.36953/
Support for spawn eggs, If ima spend 5 bucks irl for some spawners I wanna easily change em to be useful fast. As for shop, if its small sounds awesome :D.
I support the shop part of the suggestion. Although, if it were to happen, then I think it shouldn't sell such rare items. Maybe use the shop was a little boost for players?