I agree with what you are saying, but I think it is important to break things up into smaller increments. It is not necessarily about logging your minutes/hours weekly and seeing whether you have improved. As you would know, sometimes it takes a lot longer to achieve certain goals eg. you cannot expect to go from benching 60kg to 100kg in a week at the gym.
I think measuring practice will assist you in forming good habits. I am aware that I am speaking to guys on this forum who already play for 4-5+ hours a day as a habit, and others who are somewhere below or even just starting but I still think the principle applies. We were taught by our parents to brush our teeth from a very young age...you might miss a day or two but you know it is something you must do otherwise your teeth will fall out. As students we want guitar practice to be the same thing (a good habit) and I think something like a log can be of great assistance.
The video recorder and mirror is also an excellent idea, and 2 weeks or more is probably a better time to set if you are purely looking for results...but if you are not practicing enough/at all then obviously you will be watching the same video every week. I think when measuring practice it should not be results based (particularly in the short term) but rather goal based...setting yourself a goal and achieving it through dedicated practice. No one ever climbed Mount Everest with one giant step...and for many of us our Everest is guitar virtuosity.
As Pebber says...a lack of effort gives you a lack of results.