They help but even when teleporting back to them you still have to traverse the entire, again randomized map again.
I believe there is a "timer" that will determine if you get a new instance of a "zone" or keep the current one when using either town portals or way points. I believe in this beta the zones are only being held for 4 minutes, whereas the "release" game will hold an empty instance for 8-12 minutes. So... I guess you have to sell/purchase really quick and get back into the instance.
I had gone through a town portal and took my sweet ass time selling and purchasing and when I went to go back into my portal it was gone, had to walk for a bit with respawned zones. Found out that the timeout was 4 minutes for open beta. Code testing...
So, in the release you should get around 10 minutes before a instance resets. That may help.