I really don't think Epcot "needed" a thrill ride. The fact that it had the slower, more relaxing and educational rides set it apart from Magic Kingdom for quite a while.
World of Motion was one of my favorites, and I miss it dearly. All of the memories I has as a kid, are just that, and I can't ever have the opportunity to experience the real thing again.
Test Track was a LONG awaited attraction, supposed to be open, not open, supposed to be open, not open........
When I finally did get to ride it, I wasn't let down. I didn't think the theming was skimpy or lacking. I did lack the theme SONG, however, which is a pretty big part of what an attraction should be.
Overall, I'd have to say that I actually love both rides, and I wish TT could have been built NEXT to WoM, but, it wasn't. If I had my choice to pick one or the other, I'd choose WoM in a second, because of those memories, and because it was a BRILLIANT example of what Epcot was supposed to be.
AND, for those who think I'm being a tad over-dramatic, I'd be willing to bet you didn't grow up riding it. I only visited once a year, but when something is there that long, it still becomes a part of you, and seeing pictures of it hurts a little. Horizons, of course, is the same story, but that's for a different thread.