We do invest a lot into tooling. There just hasn't been a huge amount of work put into IDE integration yet. There's lots of other types of tooling: Cargo, rustfmt, clippy, Racer, good error messages…
The only "critical" thing missing from this list would be a rustfix. Sadly, this is probably only worth it once the AST/compiler plugins are stabilized.
Well, rustfix is useful when we're breaking code, but we aren't doing that anymore, other than deep soundness fixes in the type system which would be very hard to automate a solution to.
