You can save the file that you're currently streaming at no additional CPU cost by saying "Save to File" in Broadcast settings. If you want to save at two different bit rates, then for the time being, it's somewhat difficult. The rewrite will make it much easier, but for now, you can run two instances of OBS by adding the "-multi" flag to the end of the Target in your OBS shortcut.
Running two encoders is only a bad idea if your CPU can't handle it. Which it very well might not be able to, but that's up to the user to decide.