Currently in your Day/Agenda view you have a palette at the bottom of the screen which has navigation functions on it. They contain buttons for Week, previous day, Today, next day, and month. These are basically buttons with text on them.
I would recommend a variation on this theme. A Navigator palette that can be turned on or off in the user preferences. This would then be available on each screen layout, not just the Day view.
On this palette you would have a Icon button for Day view with hours (future feature) - (Which defaults to the current day - "Today".), Week view, Month view, Year view?, Agenda view, Task view (Since your adding that future feature too). There would also be an icon which allows you to toggle/switch to alternative layouts. Say you end up having 3 variations of a week layout. Touching this icon toggle for layouts switches you between layouts for a particular style such as week view.
The icons for Day view can be a small calendar with an orange highlight for one day, The week view one an orage bar accross one week, the month view orange over a whole days worth in a month, etc.
I find this type of palette very easy to navigate between views. And I find the next or prev buttons kind of redundant because your expecting to use gestures such as side to side to go to Next or Previous. So I feel these can be eliminated.
Please do not get me wrong. I think your way of navigation is very good. I just think that navigator palette can be enhanced in function and looks and be used on the other layouts if they desire to display it.
Just my 2 cents