The upstairs bathroom in my 1925 bungalow has plaster walls / coved plaster ceiling. It looks like at one time the ceiling may have had embossing of some kind (there is some rose embossed plaster elsewhere in the house). At this point though time and several layers of paint from previous owners have taken their toll - there are some cracks due to moisture damage and the embossing just makes the ceiling look lumpy. The plaster does however seem to be otherwise in good shape (no separation from the lathe that I have found).

I'd to get this repaired (and then install a vent fan so there are no more moisture issues) but I'm not sure what exactly needs to be done. I think a skim coat and spot repairs would even things out, but that seems like asking for trouble over old paint. What's the most cost effective way to get this cleaned up?