while clonazepam and alprazolam are equipotent the drugs work very differently, Clonazepam is generally used in treating general anxiety, it has a long half life and a slow onset, so it lasts much longer than alprazolam (xanax) which is used primarily for panic attacks and has a fast onset of action and a short half life. You might find yourself experiencing interpose withdrawal if you switch to just .5mg of xanax twice a day, it might do you better to see if you can get 2mg/day prescribed, then you can take .5mg 3-4 times or 1mg 2x, just my opinion but I do have a lot of experience with benzodiazepines, you also have to keep in mind though that if you were to raise your benzo dose just to be mindful of the fact that you're also on methadone, and mixing CNS depressants can be dangerous, though definitely doable if you're responsible.
I'm kind of curious why diazepam (valium) is being used for insomnia, its a great benzo but it's not one of the hypnotic classes, temazepam is much more effective (and equipotent to valium, or at least close) than diazepam. In fact, Valium would probably be the better benzo to use for anxiety, its got the fast onset and the long duration of effect that clonazepam has and 10mg=.5mg clonazepam.