Question: Midichlorian's are chemical compounds found within every living cell that forms the basis between the connection life and the Force. Without midichlorians, life would be impossible. The amount of midichlorians in a life form represents its ability to understand, comprehend, and manipulate the Force.

My name is Darth Incognitus, and I have decided to absorb more of these cells into my own body to make my force sensitive abilities stronger. To accomplish this, I have kidnapped numerous force sensitive users who match my blood type. When their midichlorian count has been measured, I will perform a blood transfusion from them to myself in order to absorb these cells. After I have attained enough of these cells, I will become the most powerful force user in the world and create my Sith empire. Then, I will use this method to strengthen my apprentices and students.

However, after a number of tries, I have noticed that my powers have not increased. No matter how many Jedi I murder and drain of blood, my abilities remain average. Why would this be the case?

Answer: 
Because the blood level midichlorian equilibrium point is determined by your body's biochemistry. You can't alter this by adding more midichlorians. All that does is cause a temporary imbalance (way too short for your body to make use of it) that your body quickly fixes. Excess midichlorian gets filtered out by the kidneys and ends up down the drain. Literally.
A blood transfusion wouldn't change the number of midichlorians in your other cells and there's no reason to think that your red blood cells are particularly important to your sensitivity to the force...especially when compared to, say, your brain cells and your nerve cells which seem much more likely to mediate between your mind and the Force. 

That being said it's actually pretty likely that such a villain would experience a boost in their ability to use the force. Combine the placebo effect with the Force and you could get some real action.