Whenever I have to work with dwgs I always import them into a document, close it, then open a fresh document and reference the first document through a DLVP.
That way I can have access to the thousands classes w/o having to deal with them in my drawing. Unless I've worked with the person who created the dwg, I usually use the dwg just as it is or as a reference to draw on top of. I usually don't try to edit. It takes too long to clean up the classes and figure out the mapping used to translate all the pastel colored lines into useful line weights.
But if editing the dwg geometry is the best way to go, look in the OIP to see what the geometry (that you can't edit) is. I've noticed that sometimes geometry comes in as a group or symbol. If it's a group, you can edit "inside" the group or ungroup. If it's a symbol you can edit the symbol, or convert to group.
hth
michaelk