If you want efficiency in making levels, you need a dedicated tool - you need to program a level editor.
No you don't.
If you want efficiency in making levels, you need to use an off-the-shelf editor, it will get you to a better level of functionality sooner. There are heaps of tilemap editors, and this game is mostly just a tilemap with various objects and metadata. It should be doable with minimum of custom code.
In order of preference:
* Use an existing editor
* Code a wrapper for existing code
* Code a plugin for existing editor
* Write your own editor
You'll have a lot more productivity if you use an existing editor, unless you have, say a team of at least 2 people fulltime generating content. And if that's the case, you won't be wasting time posting on gdnet.