We're thinking about a similar upgrade (8.x to 10d) but the cost of upgrading the remote agents is prohibitive; each agent upgrade costs as much as the BE upgrade itself, and we have several remote servers which already have paid-for 8.x agents.
Do we really need the remote agents? We're only backing up shared data on the remote servers, and could use the backup built-in to Windows 2003 to save the system state locally to a shared folder, then back that up using BE.