Need to allow admin users to place and modify command blocks without having 'OP' as it is disabled.

If you're using Sponge, you get access to two permission nodes

Allow editing an ordinary commandblock of the given name: minecraft.commandblock.edit.block.
Allow editing a minecart commandblock of the given name: minecraft.commandblock.edit.minecart.
As well as a spawn protection bypass.

using spigot, would it be better to switch?

Spigot doesn't have a permission for it.

Switching server APIs is ultimatly up to you.
Most Spigot plugins and mods won't work on Sponge, but in many cases there is already a Sponge or Forge replacement.
There is a slight learning curve when switching, but I personally think it's worth it.

Installed a bukkit plugin that provided the permission nodes https://dev.bukkit.org/projects/commandblockperms