Loose rivets your post has summarised the point very well. In the eyecare profession "eye exercises" are a very important aspect of certain treatment modalities. For example eye exercises for certain types and stages of "squint" (tropias and phorias), amblyopia (lazy eye), convergence insufficiency as well as a range of accommodative disorders are commonplace. Their efficacy is also well researched and scientifically proven.
However, the results of the use of "eye exercises" to try and treat a refractive error such as myopia or hyperopia is not well established. Although exercise techniques may certainly help aid the function of the ciliary muscles controlling the lens; the use of such exercises to treat a refractive problem does not address the aetiology or cause of the problem. Simply, a refractive error such as myopia or hyperopia is essentially due to the eyeball being too long or too short in relation to the power produced by the cornea. Therefore eye exercises will simply not be able to reposition the focal point of light back onto the retina where it should be.
In the case of presbyopia which occurs at around age 45, where one tends to need reading glasses, the cause of this is very different. A review of the mechanisms of accommodation and the development of presbyopia indicate it unlikely that a loss of strength of the ciliary muscle in the eye is the cause of presbyopia. On the contrary in fact, the literature demonstrates that the muscles in the eye are actually stronger at age 50 than they were at age 15 thereby negating any theory that the muscles get weaker as one gets older. Rather, the flexibility of the lens in the eye is reduced due to its increased growth throughout life as well as lens sclerosis. Another aspect is that because the lens continues to grow throughout life, there is less and less space available around the lens for the muscles to exert their mechanical traction and therefore accommodation is reduced. This loss in accommodation takes place throughout life (commensurate with the growth of the lens) and the rate of change is well established scientifically.
To sum up, eye exercises are a very useful treatment option for certain indicated eye disorders. But there is little scientific evidence to suggest that eye exercises offer any improvement for purely refractive errors or presbyopia.