as you noticed, two issues (you can already cherry-pick them) will help you to display more information :
* MDL-29435 (return debug information for SOAP/XMLRPC server)
* MDL-29277 (return the path of the value being faulty when the error is about a parameters or a return value not matching the function description)
I also understand you concern about bulk functions that stop the execution when one "element" is faulty. I've just wrote an issue for that (MDL-29776) and I'll put it in the list to improve.
Thanks for your report.