David
If you think you have a good image I would definitely go for another version. I've found there are certain scenes which go down well (it's not always the ones you expect either) and if I have something which either sells quickly or gets loads of hits I'll do similar ones in different sizes/formats/mediums. I always go back to the source photo or image each time though and each one will be a bit different - copying an old painting would definitely be a step too far for me!
On hits, I find paintings seem to "take turns" to be the most popular, it's the same on my MG site as well. Over the last month or so my most popular image on TAW by far is the Young Ballerina (actually my daughter!) which I posted here a few weeks ago - it does make you wonder if there's any connection between posting on a forum and loads of hits. No buyers yet though .....
Elise