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

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.

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?

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