Hey ddogusterion
You asked: "Why would taking it on several different days raise efficacy?"
My doc said the same thing, when I pressed him on it, he mentioned half-life, and also theorized muscle memory since V relaxes smooth muscle tissue.
As mentioned before in this thread, a common positive effect of V is better response the next morning, indicating that the drug is still active. Here is why.
A simple example of half life (for V, half life is 4 hours) that means in 4 hours your body will have eliminated half of the dose. That does not mean that it is gone completely in 8 hours. The next 4 hours eliminates only half again.
For example, if you took 100mg (make sure not with fatty meal as it lowers absorption dramatically), 4 hours later you will still have 50mg biologically active, which is still a very effective dose. At 12 hours later, you are down to 25mg which is the lowest prescribed dose, 16 hours 12.5mg, 20 hours 6.25mg, 24 hours 3.125mg.
If you take it again on the 24th hour, you start out with 103.125mg active, and work the numbers from there.
Again this is an oversimplification of the process, but it is the same reason that on some antibiotics they tell you to take a "loading dose" of two pills the first day to get your serum level up to the point where it becomes biologically active enough to combat the infection for 24 hours before half life lowers it below therapeutic levels before your next dose. It is also why some substances are detected in blood tests, weeks or months later, they have longer half lives.
Some links:
Biological half-life - Wikipedia
Sildenafil - Wikipedia
Also, I have found that the aches are dealt with very easily with ibuprofen and that your body will become accustomed, and they go away with regular use