Hi Trouper,
Although I see that there are many other posts regarding this topic I am new to this forum and wanted to add my personal experience with this topic in hope that it will help you.
When I was 16 I started using a vibrator that was similar to the hitachi magic wand. I became "addicted" to it and used it in the same way you did, to achieve orgasm after orgasm until they were so slight they didn't do much - the more per session. Eventually I went away to college and brought it with me and used it there. When I was 19 I met my then future/now ex-husband who asked me to stop using it. I made jokes that my clit was numb because at that point I could not have an orgasm any other way and could barely even feel it during any type of manual stimulation. However, I threw it out and after awhile, a long while actually - the sensation came back and I was able to have orgasms by manually stimulating the clitoris and for a short while (many years later) I even experienced vaginal orgasms.
I have tried to use vibrators on my clit very few times since then, and it has been a good 20 years - but I've never liked them, they hurt now. I have continued to use my fingers or my partner's fingers or oral sex as well as other sex toys and I have never had the "numb clit" problem since. It takes awhile to gain the sensitivity back, but it's well worth it!!!!!!!!!!!
I have 2 other female friends who are reliant on the hitachi wand and cannot have orgasms without it. One is in her 40's and the other in her 20's. They have both used the hitachi wand exclusively for many years and even during partner sex must use it to achieve orgasm.
Howard Stern used to say the same thing about his wife (now ex wife) joking that she formed a callous on her clit from using a vibrator.
I have no doubt that there are healthy ways to use a vibrator that don't cause desensitization, however not everything works for everyone.
Hope this helped a bit