Its difficult to find information about it online (thanks drug companies), but if you do real research into medical journals, Moderate doses can lead to long term/structural changes in the brain. Abuse can be neurotoxic. Ritalin is considerably safer than adderall/dex. This makes it hard to separate out what was caused by the drug and what is a symptom of ADD, thus causing a bad feedback cycle.
I recently saw a therapist (for unrelated issues) who said it was a common pattern for bright individuals who were bored with regular schooling to be diagnosed as ADD.
Meditation, exercise, proper sleep, and healthy food all have a huge effect. Biggest thing is being interested in what I am working on at work. I drink huge amounts of caffeine and sugar (soda helps the most), which help a ton. I take frequent breaks, go for walks, and work obscure hours. I end up getting about 4 peoples work done myself, mainly because I can leverage my programming ability to find shortcuts in the work that other people cannot.
The behavior & personality change (more generally, neuroplasticity) is a very interesting aspect. I have most definitely not stayed the same. Doing anything every day will lead to long-term structural changes in the brain, meditating, making music, playing sports, coding. When we desire those changes we call it expertise. Behavior change was my explicit reason for taking Dexedrine in the first place and I'm happy I have successfully brought about (some) of the desired change. As for unwanted changes, I'm still happily married and my closest friends and family have remained close so I see no evidence of the changes being harmful enough to outweigh the benefits.
Nobody is the same person we were 10 years ago, whether they use drugs or not. On the other hand, I worked in harm reduction and addiction services for 15 years, and I'm not about to deny that issues with addiction and impulse control are very real and dangerous challenges for a subset of amphetamine users. Kudos to you for noticing and addressing the issues your use was leading to, I bet it wasn't easy.
I'll stand with you and say that getting ADD treated with stimulants is very much like lighting a fire. You can generate the energy you need, but you can also get burned. There is no cure all, mileage may very, etc.