Thanks for the suggestions! A couple of things which may be of use to you regarding wet paper:
1/ The watercolor tool has a 'wet paper' setting in the settings panel. Turn this on to simulate using watercolour on wet paper. This won't change what's already on the canvas but will make new strokes act as if the canvas were wet.
2/ If you want to wet an area, instead of the above, you can use white watercolour, or watercolour of any colour if you set the 'thinners' value in the settings panel to 100%. This allows you to basically paint water on an area of the canvas. Watercolour applied to this area will look dilute in the centre and will react more dryly when it hits the edges.
Resident Bug-Hunter and Support Guy