I realize I failed to mention a couple other examples of how the concept of "internal improvements" applied to Abraham Lincoln and his life, and suppose this is a topic so large or potentially large that I probably should do thorough research on it instead of writing about it from the top of my head, but, as Lincoln may said himself "that cat's out of the bag."
The first, and probably best, example of Abraham Lincoln seeking his own "internal improvements" was his self-education, borrowing books from neighbors, reading whenever he could find time, repeating talks he heard adults give until he could comprehend them well enough to interpret them for others his age and, as he reached adulthood, his studies of the law and of the books of Euclid, the mathematician and logician whose books are among the most influential ever written. For Lincoln to learn Euclid on his own required an incredible amount of work, effort and thought, and may be the ultimate example of how "internal improvements" were the basis of Lincoln's overall mindset and not just in economic or political theories.
The other example that came to mind is from Lincoln's Presidency. As the Civil War started, Lincoln was Commander-in-Chief, but had virtually no military training, other than a brief spell in the Black Hawk War in the early 1830s. His formal military education was even more lacking than his formal schooling was during his childhood, but, again, Lincoln attacked this problem and resolved it himself through the study of military manuals and other books concerning tactics and militaristic matters.
Here I will quote Tried by War: Abraham Lincoln as Commander in Chief by James M. McPherson, copyright 2008, Penguin Press. In the introduction to his book, McPherson discusses Lincoln's quest to master military matters and quotes Lincoln's secretary John Hay.
"He gave himself, night and day, to the study of the military situation...He read a large number of strategical works. He pored over the reports from the various departments and districts of the field of war. He held long conferences with eminent generals and admirals, and astonished them by the extent of his special knowledge and the keen intelligence of his questions."
Clearly, Abraham Lincoln displayed the ability and instinct to improve himself through education, most of which was done on his own time and with his own effort. Nothing can be more demonstrative of "internal improvements" than this constant self-education - whether in reading, understanding language, grasping the study of the law or Euclid, or gaining insight into military tactics and theories, but his growth and development in other aspects of his life such as religious/moral beliefs and his thoughts about race relations and the place of African-Americans in American society also display a definitive growth that can be categorized as "internal improvements."