I have an idea: If you are trying to get mobility and dexterity back, focusing on speed is only one aspect of it, I feel. Coordination is a huge aspect. Try picking up coins and putting them in a piggy bank. I know this sounds idiotic, but you might be surprised, especially when you do it with your non-dominant hand. If this isn't challenging enough, try it with pieces of rice. You said that you If you want to build strength, put a weight on your wrist. Use your imagination. Make up exercises similar to this.
Hope this helps!