AMG, it seems the issue is structural interferance as long as when you go outside the signal is significantly improved and it appears to really only be an issue at your residence, for the most part anyway.
Considering that, your best bet is to call Sprint again, tell them politely and rationally the issues you are experiencing and that something may need to be done or you have no choice but to cancel and go back to your former provider (no names), which you already know works well in your home because the issues are affecting your work, job or business, first and foremost. Otherwise the device is great and the customer service has been excellent SO FAR but the coverage specifically in your home is the only real issue.
Inquire if anything can be done if they didn't already suggest something and they will likey mention the airrave but if they insist you have to pay for it and it's service tell them that only defeats the purpose, as any money spent on that could simply be used to get out of their service and into something else, AGAIN, that you already know works better in your home and you have no issues with. After being told or asking about the cost, tell them the airrave would cost $100 up front and another $110 or $115 in monthly charges for the remainder of two years and it would be cheaper to sell the phone and leave, not that you necessarily want to.