About the [@item[@0..$#item]] thing...no reason other than using the supplied example from the docs (after all, good enough for damian, good enough for me). chromatic caught this when I posted, I checked and as you say, there is no difference other than less typing!
As far as the #15 goes, the problem is that the grammar file has no way to contain the RD_AUTOACTION specification with the command line as given. I also played with the expanded .pl version but still couldn't get it to provide identical behavior. What did work was the suggested sledge hammer approach--fix each instance by hand! There may have been a discernable pattern to what was used as default, but I didn't see it and didn't have the time to track it down.
I like your final 'additional suggestion', the Parse::RecDescent version of 'do as little as possible to get the job done'.
"Never try to teach a pig to sing…it wastes your time and it annoys the pig."