frenchy, FWIW, I'm addressing the same question, but in a different way. I'm offering up my approach to the issue and my underlying thought process not to criticize your approach but rather to illustrate a different way of approaching the same problem.
My ultimate goal is to be "highly competitive" in RRs and TTs beginning next Spring. I never much enjoyed crits when I raced before and I doubt that I will fall in love with them this time. I enjoy TTs because of the ability to use all my skills, both mental and physical. When I raced before, I was a good climber and only a fair sprinter. I'm guessing this time won't be much different, so I imagine I won't win many races if there are lots of guys still with the lead pack at the finish. My favorite RR would be ~100 miles with about 8 major climbs and a 10-mile climb to the finish. But, there aren't any of those for masters, so I'll have to settle for being in the lead group (hopefully) and watching the sprinters battle it out for the win. TTs are a different matter, and I want to be in contention for the win in most TTs. I have translated these objectives into power goals based primarily on a review of winning TT times in my geography. It looks to me as though if I want to be highly competitive I need a 40K MP of ~375w, but 350w would probably allow me to be with the lead group in RRs. So, I suppose my ultimate goal is 375w.
I have no idea if that is feasible for me by next Spring or the following Spring or ever. But, that's irrelevant now. All I need at the moment is a short-term goal and a plan to get there. After that, I'll set a new goal and develop a plan to get there. At some point, I'll stop improving and that will be that. I think improvements in 40K MP can be viewed in five degrees of difficulty. The first 100w is basically "free." Unless one has a physical disability, anyone can get on a bike and produce 100w. The next 100w is also very easy. Just spending >3-4 hrs/wk on one's bike at 75%MHR should result in 200w. I don't think one needs to do intervals at all to get to 200w. The next 100w requires some form of interval training, but I think almost any combination of intervals up to and including 300w efforts twice a week will get you to 300w. At 300w, I think progress becomes much more difficult and thus the training program needs to be more carefully designed, nutrition becomes more important, etc., etc. And, very importantly, I think progress >300w is no longer assured regardless of the genius of the training plan. And, that's precisely where I think I will be in about a month. Oh, yeah, the fifth level? Well, that's >400w and I don't think I will ever face that problem.
Beginning at 300w, I plan to set goals and a training plan in 25w increments. My plan will not be time-driven but rather program-driven with no time cap. IOW, I will design a training plan designed to get me from 300w to 325w and will follow my plan and track my progress until I reach my goal, however long that is. Then, I'll design a plan to reach 350w and so on until I stop improving. Then I'll celebrate because I will have reached my own personal Mount Everest -- I'm as good as I'm going to be. Yahoo! How many times in life can we say we have taken ourselves to our personal limits? That'll be a cool day. Then, I'll take my power (whatever it is) to the course. I'm sure I can be competitive in some citizens races if they have age groups.
My biggest issue at the moment is deciding whether to get a coach for this next phase. Like many things, it is a question of cost/benefit. The main alternative I am considering is to take a course such as that offered by Peaks Coaching Group (with no less than Andy Coggan lecturing on physiology) and be my own coach. Or, after taking the Peaks course I might know enough to know that I need a coach. No offense to you coaches, but I think Bozo could have designed a program to get me to 300w. But, now comes the hard part and Bozo might not cut it.