Two suggestions for syringes:

1. Have the creative inventory and/or JEI contain all valid filled syringes in addition to the empty one
2. Have their tooltips show their required resources

2. What required resources do you mean?

The key, block, and living material required to actually do the spawning.

You can see that in the spawner. Note that the syring is not only for spawning so it wouldn't fit there really

True. I was only thinking about its use in the spawner and not its other uses. I guess I really only want the JEI suggestion then.