The graph below clearly shows the tonnage passing through the lock gates north of Münster.
Despite the attacks that began in 1940, there was an inexorable increase until the raids of 1944 and the massive attacks in early 1945 that totally closed the canal to any traffic.
It is quite possible that the rise would have greater without the attacks but, if the British aim had been to inflict a "fatal blow" to the German war effort, it did not succeed until 1944/45.
In my view, the plan to deliver such a blow in 1940 by destroying the aqueducts over the River Ems was flawed. Traffic flow would most certainly be 'incommoded' by the loss of one or other of the two aqueducts but, to achieve maximum denial of the canal, both crossings would need to be put out of action at the same time.
Recent research has also cast doubt over the influence of the canal raids on the preparation for Operation Sealion.
English translations of the war diaries of the German Naval Staff state that the raids of 1940 were a factor in causing the invasion to be shelved. However, when reading the diaries in the original German, this factor is missing!
The requisition of barges for the invasion only began in earnest in mid-August 1940 and the vast majority were moved to the invasion ports by routes other than the Dortmund-Ems Canal.
After the war, Albert Speer (in his book Inside the Third Reich) wrote that of all the strategic attacks made on Germany, the raids on the canals had by far the greatest effect on the German war effort. However, he may have felt that this was something the Allies wanted to read.
Bomber Harris, in his speech at the RAF Bomber Command Reunion Dinner held in London and April 30th 1977 also spoke about the effect of the bombing on Germany's ability to deliver prefabricated U-Boat sections using the canals.
As a final comment, it should be remembered that a large number of troops were stationed along the length of the canal in order to defend it. Maintaining such a defence required significant resources.