If you want to have a nice spawn but are worried that people might grief it then use this plugin. It prevents block breaking. In the futer I will make one that prevents block placing as well.

Comands:
/blockbreak <enable/disable> - Toggles breaking blocks for all players.
/bb - <enable/disable> - Toggles breaking blocks for all players.
/toggleblockbreak - <enable/disable> - Toggles breaking blocks for all players.

Permmsions:
noblockbreak.toggle.command

Note all players including ops will not be able to break blocks. If you wish to, close your server then do so with a whilist on. This prevents others from join while you make changes.

!!WARNING!!
There is NO config file meaning Restarting/Reloading your server will automatically make blocks not mineable.

https://youtube.com/mjdawson