Short answer: I did clean coils starting out with varying degrees of success. I wound up deciding it wasn't worth it as a) they tended to have unpredictable life and I would neve know when it would die again, unpredictably, and burn a tank full of juice between 24--48 hours later and b) I wasn't really sure how well they were getting "cleaned."
I think it's probably okay to clean some of them. How much extra life will be debatable.
If you can move to rebuilding it may be less expensive for you and I found with more rebuildable tanks in my arsenal, keeping the drop in coil tanks I REALLY liked, and since I'm using them not 100% of the time and rotating setups, my coil life has improved OVERALL because my tanks aren't overheating. I do like RTAs and even take some out of the house (now) but there will probably always be at least a FEW drop in tanks in my arsenal, unless the vaping hammer descends.
There is a learning curve with rebuildables so I'm glad you are asking about it on another thread and etc, as if you can get going with rebuildables it should help your coil costs considerably.
I might try unflavored to see if you like it, at least in your drop in coils, it should extend their life considerable, although I consider chain vaping in VW mode to be equally a coil killer due to increased heat in the tank (obviously, this too can vary and depend on a lot of factors) but it's good to have backups, so you may want to keep this tank "in service" so to speak.
Best of luck, I don't know much about cleaning ceramic other than a vague idea that it's not a good idea. Etc.
Best of luck,
Anna