I have had similar job sin the past where I have had to clean up solutions and found this tool to be extremely helpful in doing the job
Its called BaseElements and it effectively analysis the DDR of your whole solution and places it all in a FileMaker database that cross references all the elements and makes it easy to find elements, scripts, field layouts etc that are not used. And it also finds any errors in the solution amongst a whole load of other things.
Definitely worth getting this tool, and there is a demo available for you to try.
I hope this help.