As far as I know, no.
You may want to avoid going by "bars", for which there is not standard, and instead use something like the app WiFi Analyzer to determine what your signal strength is. If you can get a signal that is better than -85 dBm or so (at the risk of stating the obvious, less negative is better), you should have a good enough signal to have a good connection.
There's no doubt that the Eris does not have a great radio, but I can get a good signal within 75 feet of my house when I am outdoors, and that's not terrible. I actually have not even tried to determine if I can get further; it's possible that I could. Even if you can get something that increases the sensitivity of the radio, the problem will be that you will also be increasing the sensitivity to noise, so your signal could get marginally better, be the same, or even marginally worse.