I have worked in this area (usability testing various insurance applications) quite a bit.
These are the most important aspects I've found via testing, and they have come up in the context of each system I've tested:
Information flow in the application matches agents' real-world tasks (there are several; interview agents and watch them work to understand this)
Data entry is fast and efficient; system does formatting and math instead of the user
System provides intelligent defaults
Questions make sense and have JIT help for terminology and decision support
System helps users feel confident that the result is correct
Inputs and outputs make sense for users' local agency systems; backend support for other systems used so no duplicate data entry is needed
Both ecommerce forms and tax-prep forms provide good (and sometimes not so good) models for complex form interactions like these.
Refer to "Forms that Work" book for usability-tested successful patterns, and when to use them:
and see also "Web Form Design" for principles of well-behaved forms
Test early and often with real agents.