Because it presents truths about human nature, "The Glass Menagerie" is still relevant, I think. It seems dated because of elements such as the merchant marines, gentlemen callers, typing classes, and public speaking courses. What is not dated are Tom's discontent and thirst for adventure, Amanda's desperate wish to ensure her children have a future, Laura's insecurities in the face of a harsh world, and Jim's sense that his best days are ahead despite the fact that he's stuck in a rut. We get those things because they're still part of who we are. Human nature never really changes.
I agree with your take on the reasons for the play's continuing relevance. In addition, the manner of escapism that Laura takes to deal with her personal difference is still relevant because people resort to various methods of escape in their attempt to avoid reality and live in an illusory world.
The play has retained its popularity because many of the issues raised in the play are still with us today. Amanda is a single parent, forced to raise two children on her own. She refuses to let Laura even mention her disability and therefore, Laura seems unable to cope with being different. Many people who are different in some way face the same self-doubts as Laura. Tom is forced into being the bread winner for his family due to circumstances beyond his control. He and his mother do not understand each other. Today, many parents still do not understand their children and vice-versa. Jim, the big man on campus in high school, finds that he is not so big after he graduates. Many former big men on campus could tell you the same story. In addition, the play says much about the attraction between young men and women and how fickle that attention can be. I think the same holds true today. Finally, the play focuses on the dreams we all have for our futures and the chance that our dreams may not come true. Especially given today's economy, I think people should be prepared and be able to face that the possibility that "you can't have it all."