You seem to be very similar to me. I honestly can't stick to a rigid program. Never have in my whole life. It's not necessarily training ADD.
Training ADD to me is more like always changing the way you train without rhyme or reason. I personally stick to a type of training and a specific approach but I must give myself options to use in my training.
I want to be able to experiment with some new methods. Furthermore I believe that someone can either have a "programmer" or a "problem solving" psychological profile.
The programmer is comfortable in a more rigidly planned program. He actually find it motivating to knows well in advance what he has to do on a daily basis. Having the whole training process planned out for a long period gives security and this can be very motivating for many people.
The problem-solver doesn't really think in the long term. Well he does in term of goal but not in term of planning. He sees the training process as a succession of problems to solve to reach the final goal. He loves to intellectualise each training session to find exactly what need improvements and nothing pleases him more than modifying his training to better address a specific thing he "discovered". He gets pissed of, or at least demotivated when he is stuck in a rigid plan where he can't devote his effort to fixing something that is not to his liking. That can eventually become "heavy" psychologically and it kills training motivation.
I'm personally of the second type. One of the athletes I train, Alex Vigneault (Crossfit athlete who just qualified for the Games) is the same way. After 3-4 weeks of sticking to a plan he starts to show signs of breakdown. If I give him the option of doing some of his stuff in his training day then he stays motivated and perform better,
I find that training geeks, those for whom the experience... learning how the body is affected by training, what method does what, practicing new techniques, is as important (sometimes more) than the actual results need to be able to play with their training to stay motivated over the long run. Force them to follow a rigid plan and even if they are getting results that are out of this world they will lose their motivation to train.
Those who thrive on a rigid training plan like to "just do it" and not have to think about it. To them training is not about understanding, learning, experimenting, it's about hard work and getting the job done. If you put them on a program where they can make choices, analyze and adapt you will take them out of their comfort zone and they will lose motivation!
Both can get results and there's been elite athletes and coaches on both side of the fence. It's just a matter of knowing your type and making the choices that will allow you to stay motivated. Be honest with yourself.
5/3/1 actually allows you to use a more adjustable approach to training. Do the main work as planned and you can play with the assistance work using various methods and exercises as long as it's rational and doesn't lead to overstress (and addresses a specific issue you have to fix).