Do ADHD drugs harm the brain? Particularly, the amphetamine "vyvanse". If one was to take a 30mg dose once a day for 50+ years, would it damage brain function at all? Would the brain simply get used to the drug and become 100% tolerant to it? Would the brain damage be permanent? Would the brain's performance be improved for the whole time taking the medication? These are some of the questions I have regarding ADHD amphetamines.
This section from the Wikipedia page on Neuroplasticity indicates (emphasis mine)


  Reviews of MRI studies on individuals with ADHD suggest that the
  long-term treatment of attention deficit hyperactivity disorder (ADHD)
  with stimulants, such as amphetamine or methylphenidate, decreases
  abnormalities in brain structure and function found in subjects with
  ADHD, and improves function in several parts of the brain, such as the
  right caudate nucleus of the basal ganglia.


The following studies are cited as reference:


Meta‐analysis of structural MRI studies in children and adults with attention deficit hyperactivity disorder indicates treatment effects (Frodl et al 2012)
Meta-analysis of Functional Magnetic Resonance Imaging Studies of Inhibition and Attention in Attention-deficit/Hyperactivity Disorder: Exploring Task-Specific, Stimulant Medication, and Age Effects (Hart H, Radua J, Nakao T, Mataix-Cols D, Rubia K 2013)
Effect of Psychostimulants on Brain Structure and Function in ADHD: A Qualitative Literature Review of MRI-Based Neuroimaging Studies (Spencer TJ, Brown A, Seidman LJ, et al 2013)


I had a quick read on these papers and they do not appear to isolate Vyvanse (lisdexamfetamine) specifically. The one from 2012 doesn't even mention it; the other two address both methylphenidate and lisdexamfetamine. Each paper has their own limitations, for instance, standardization concerning comorbid conditions, age, etc.

From what I can understand, long-term use of ADHD stimulants in individuals with ADHD (this is important) does not appear to be associated with brain damage, but rather the opposite, they appear to promote "normalization" of certain structural deficiences. Not all deficiences, though (i.e. effects visible on the right anterior cingulate cortex (ACC) but not on the left ACC).

The paper from Spencer et al cites another - Potential adverse effects of amphetamine treatment on brain and behavior: a review (Berman, Steven M. et al 2009). I didn't have a chance to look into that just yet.