No doubt Elise's are incredibly fun cars, and gorgeous to look at. Did you get to drive it at all? I can't imagine much out there being more fun at a track. Though practicality it probably won't be able to hold a candle to a Subaru.
It's unfortunate that it'd cost that much more to remove the spoiler on an STI. While I love STIs, I do agree that a nice trunk lip would look the best. I've seen a couple and they look better than anything on the new Sedans. Honestly though, you could probably offset some of the cost by selling the STI spoiler on the forum classifieds or Craiglist...or if you can wait, find a trunk swap buddy, considering there are threads for that. Just throwing that out there for ya.