I suppose you could use a giant crystal with smaller crystals around it. Still, I think any kind of interactive interface would be funner then just clicking a picture on a graph. There could be an indicator of some sort as you mention or you could be following a recipe one of your adventurers find while on a quest. There's lots of things you can do with it honestly.
It's not as much the user interface I'm opposed to as the mechanic itself. It's either too vague and random, or it takes something that should be simple and quick and turns it into a mini-game that would be fun the first few games, but quickly start to get old.
Now... if Stardock does allow us to dynamically create or combine spells of our own... That would be awesome (I cannot emphasize how awesome that would be). And having an interface like this, provided it acts as an intuitive medium for such design, would be much more palatable to me.