That sounds very familiar. We are wrapping up the first phase of a project that has lasted about a year to get away from that very same 3rd party design. It had about 90% of what you mentioned plus it has an inheritance design with all objects deriving from the same base table so that table became very contentious. In addition to that there were no keys on the table and it took a minimum of about 6-12 months before most were able to start to understand the design.

We fortunately have it mostly under control now. We've taken saves and opens from 10's of thousand calls in sql profiler down to about 100. We used .Net DataTables and SQL Server DataTable Types. We've got the save/load times down by abuot 80% and prob about 90% or more when we can get rid of the third party parts completely.

With the right brain power, and a little bit of elbow grease, it is possible to tame the beast. The one positive thing about the poor database design was that my SQL Skills have improved tremendously because you really had to rack your brain to find the data you're looking for.