In a conversation with a friend of mine, he told me that there were several plots to assassinate Hitler during WWII (both before and after Normandy) that were abandoned. The rationale was that Hitler was a terrible strategist and keeping him alive would help to ensure Allied victory in Europe, but if he was assassinated he would be succeeded by (potentially) a much more competent general. Is there any truth to this?
I believe your friend is correct. The Special Operations Executive (British secret service) bought an assassination plan quite near to fruition (Operation Foxley), with a Polish agent recruited ready to take the shot and to die in the process.
It was submitted in 1944, and Churchill approved of the plan, but wasn't carried out for precisely the reasons you stated- the ULTRA intercepts gave the Allies an idea as to Hitler's influence on strategy, and obviously they judged that it was better for him to remain in place. A decision I agree with.