Not yet read the whole thread, but when we replaced the CH we used a towel rail in both upstairs bathroom and downstairs wet room.
It very much depends on how well insulated your wet room is and how warm the rest of the house is. The downstairs towel rail is 600 * 1000 and very rarely comes on. The room is roughly 1800 * 2300 but has no outside walls.
The bathroom towel rail is roughly 600 * 1150 The room is roughly 2300 * 2000 with one outside wall with a window. We are in a semi.
Both rooms can be heated to toastiness by the towel rails quite easily. Noted that we don't lag them completely with towels.
In our previous house we had a small bathroom radiator and added a traditional towel rail above it (that is big chrome pipes far apart, not loads of small pipes close together). This again worked very well. In many ways it was a better solution but it did look a bit ugly.
Cheers
Dave R