I really like to know why you were downvoted, because I made the same observations you did and basically came to the same conclusion. I'd add the really bad IDE support. I've met some developers that said the only thing that kept them from leaving Groovy was that Grails and Spock are really great and worth the trouble. Other than that I see Groovy's future more as a glue language and as a language for tools. Which I'd find very unfortunate because I like Groovy's simplicity & flexibility as a JVM language.
I tried to install the Groovy plugins on a default Eclipse installation and never got the same result I got on the bloated default GGTS installation. But even with GGTS I had a mediocre experience at best. I tried the commercial version of IntelliJ two years ago and it was okay, but still lacking compared to the Java autocompletition. I'm really happy that the situation is better now.
As I use Groovy more of a host for DSLs (like Gradle or Spock), I hope tooling for this areas will improve. In my eyes, this is Groovy's sweet spot.