Lots of wisdom in the posts above. I enjoyed reading the responses and felt they were all quite solid.
I may look at your questions differently though:
My question now is: Is the presence of a flaw in a port the most important item to you when you make a TN?
When I create a tasting note, I look to provide information on the coloration of the wine to give an indication if it was youthful or showing signs of maturity. Then give an indication of the aromatics, flavors, body weight, structure, texture and finish ... usually a drinking window. That's what I like to include when time permits. But ultimately, what counts most is conveying whether or not I enjoyed the wine or not. A tasting note can be as simple as "I loved it" or "this really was not to my liking" but you get the picture. As to a flaw in a wine, whether it is: cooked, VA, devoid of acidity, TCA, oxidized, Brettanomyces etc., should be noted in the TN to provide the backdrop for others to understand there was something wrong. It may take a specific individual years to be able to tell what the flaw is derived from, and sometimes they never do learn that. Either way, most people can tell when something smells or tastes "wrong" and that should be conveyed in the TN, even if it can't be explained. That said, I do NOT go looking for flaws in Port or any wine I drink. I note them if they are present, as mentioned, but I don't look for them or hope to find them.
Now comes the personal philosophy of the reviewer. Is the glass half empty or full? I choose to try to find something good in every glass of Port or wine I taste. I may rate it 80 points, but will still try to find whatever characteristics in the juice that seem to be good and make sure to include that too. I truly do not like to read wine reviews that seem focused on finding flaws or the negative aspects of wine ... and there are many that I have found who do come from the 'glass is half empty' direction and it becomes tiresome to read. I am not advocating making everything bright and cheery, when a wine is clearly no good. I am just sayin' that the majority of wine is sound and there are going to be things that can be picked on if looking to do so ... in just about every wine. However, it is so much more enjoyable to read about what someone found in their glass to really enjoy.
And do you really enjoy a glass of port better when it has no flaws?
Of course. Who wouldn't prefer a near perfect glass or bottle of Port? But depending on the seriousness of a flaw, it can be overlooked, or "compartmentalized" and the Port still enjoyed. I recently had a 1977 Taylor here that was slightly corked. Most couldn't detect the low level of TCA, but it was immediately apparent to me. The good news was that it was still fairly light and allowed for the aromatics and flavors to still shine through. I was able to drink past the obvious flaw and enjoy the VP nonetheless. Sometimes that is just not possible, but in this case, I was able to 'drink around it.'
Does it make a port more/less enjoyable for you?
Depends on the issue. Most flaws detract from the experience and in evaluating a wine, the flaw will lead to a lower score than if it was a perfect bottle. But as mentioned above, it depends on how serious the flaw actually is. Sometimes, a flaw ... like VA (aka = volatile acidity) is something in low levels that may make a wine better and provides for lifted or high-toned aromatics in a Port (moreso Madeira) which I can find enjoyable. So, it not only depends on how flawed, but which one for which wine. Given my druthers, I would much prefer a wine without a flaw though.
Can I f.i. say that the Vau vintage lack's complexity (for me) and that would be a flaw i.m.o?
There are flaws which are chemically induced, or introduced by poor winemaking or even viticulture. Those are flaws that if in a wine, you can't help but notice when trained to do so. For a beginner or someone who is not as experienced or "immune" to a particular flaw or the majority of them ... this person might find the wine is not to their liking but they just don't know why. That's ok too. But something like the wine lacking complexity ... is not really what I'd call a flaw, it is just the natural character of the wine, as experienced by you. Someone sitting next to you might find it the most complex wine they've ever tasted. So, my "must buy" might be your "pour down the drain" and vice versa. What counts most is how the wine smells and tastes to YOU and the impression it leaves on your palate. But don't think that any/everything you don't like is a flaw.
Last but not least, for me ...
look for the beauty in every wine, when possible. It just makes life and wine, that much more enjoyable.