I think you misunderstood me, I wasn't implying that your engine would be hard to use, just that some I've used in the past were ridiculously complex and under documented.
I think using speadsheets is fine for data, but how are you going to handle more complex things like maps and events? Editing those in a spreadsheet would be a nightmare.
No worries. :)
For maps, I plan on having a WYSIWYG map editor -- there's not really much way around that. Nobody wants to edit maps using Excel, and I think writing a map editor will actually be easier than coming up with a text format that even remotely makes sense.
Events are the one thing I'm still thinking about in terms of the design framework. I have pretty much everything else hammered out, and I'm to the point of beginning to write the map and battle engines, but it won't make for a very interesting game if you can't even rescue Sara to get the bridge built.

I do have some experience in parsing scripting languages, though, so I may roll my own event script. I don't think I want to try to implement something as complex as Ruby or Python support. I would really like to be able to edit scripts visually, but that requires writing some pretty sophisticated tools.