Here are some ideas for functions/options that would be nice to have,

Options/Function:
Add Disable required Player //That mobs can spawn even there is no player within 128 block or even on another dimension
Add Disable spawn requirements //That mobs can spawn even there is light or water
Add Increase/Decrease MaxNearbyEntities
Add Disable spawn egg drop for Mobs spawned by spawner or spawn egg

Possible items that can be used for the options above:
Dragon Egg
Nether Star
Enchanted Golden Appe
Ghast Tear

Additional ideas:
Add the number of entities in the GUI for SpawnCount <number of entities to spawn> like SpawnRange (same for Speed would be nice)

The reason why I didn't add numbers for count and speed is because they depend on multiple variables. Therefore it's hard to have a specific value like range has. I think it becomes less confusing for casual players to use. Even if the count is, let say 8, it does not mean there will be 8 spawns each time. However, I could add a detailed screen showing the exact spawner parameters.

Thanks for the suggestions.

Thx for your fast reply.
I can totally understand why you have done it at this way, if it is too much work or too hard to implement it's not necessary but would nice to have for ppl like me :D

I second the active when no player nearby one.