There are two schools of thought when it comes to the care of stencils. Some artists do not like the bother of cleaning off the paint and dyes after they have used their stencils. Others like to clean them after every use. I'm in the latter category. I believe one gets a better looking design when the stencils are clean.
DecoArt Media just came out with a product called Brush & Stencil Cleaner. And I am very impressed. Yesterday, the above stencil (Old French Script) was heavily encrusted with blue acrylic paint. I used the cleaner and the stencil looks new. I just have to go back and wipe off a few specks of blue.
I also used the cleaner on some other stencils that had some stubborn, old acrylic paint stains on them - and they now are stain-free. I believe you will like this product.
(Full Disclosure: I am a member of the DecoArt Helping Artist Program. However, I only endorse products that I really like and regularly use.)