We are trying to improve the experience of this area of our application so that even if it's cached, you won't find it frustratingly stale. One of the UI elements we are experimenting with is giving you the ability to refresh the performance of whichever position you want, whenever you want.
When you login today, you'll see that on any of your positions on your dashboard you can hover over that row and then click the performance indicator (the up/down images) or the refresh link below it to get the cache refreshed with the real time performance. For example:
There are many more improvements we have planned for the dashboard. Stay tuned. And have a very Happy Thanksgiving!