Update: Having now worked with ST2 more longer now the performance challenges on Android are just something you have to accept. There are many things you can do to avoid performance issues such as reduce listeners and events, keep your DOM light (below 2000 nodes) and generally avoid any CSS3 transformations and effects (these in particular don't perform well on Android)
Another thing to consider is rather than using the built in WebView you could use the CrossWalk browser and embed this in APK.
https://crosswalk-project.org
It adds a little size to your APK (15-20MB), but it performs better than the built in WebView and brings stability and consistency to a very fragmented platform. Consider the reality that every WebView on Android depending on device, vendor and OS version may be different in small ways. CrossWalk will allow you to have the exact same version across all Android 4.0+ devices and remove any device or vendor specific issues.
There is no silver bullet for performance on Android. Graphics acceleration won't improve the perform of pure javascript execution or DOM manipulation. If you want to understand why, then start here:
What's the difference between reflow and repaint?
Older Answer (may still be valid):
For ICS and above the following setting on the webview will significantly improve rendering performance for Sencha Touch on Android:
mWebView.setLayerType(WebView.LAYER_TYPE_HARDWARE, null);
However in my experience this will introduce artifacts into CSS rendering depending on the device and platform variation. I haven't specifically found a reason for this and I don't expect Google will resolve it as the webview component will be getting replaced with a newer and better version in Android 4.4.
https://developers.google.com/chrome/mobile/docs/webview/overview