I have complained about IPAM's discovery process many times but I think I have finally come to a consolidated thought process on how I would like it to work.
The idea is pretty simple really. Have IPAM do something similar to that of the toolset program Subnet List.
Just attach to a router or routers and import their routing tables WITH subnet masks and do a direct import on that.
If you are like me and you have some summary addresses I figure you can connect to that site and pull in the local tables for the individual subnets.
Then IPAM can do something to the effect of just going with the longer subnet mask if their is duplication IE 10.1.0.0/16 gets pulled in via summary but the 10.1.0.0/24's get imported because they are longer matches.
Just my 2 cents.