[HTC EVO 3D] liamstears:
Just from looking at your line I see an error

This:

<TextView android:textSize="@dimen/clear_button_font_size" android:textColor="#ff58AAD0" android:layout_gravity="center" android:id="@id/clear_all_button" android:background="@drawable/btn_default_small" android:paddingLeft="0.0px" android:paddingRight="0.0px" android:layout_width="fill_parent" android:layout_height="40.0dip" android:text="@string/status_bar_clear_all_button" style="?android:attr/buttonStyle" />

Should be this:

<TextView android:textSize="@dimen/clear_button_font_size" android:textColor="#ff58AAD0" android:layout_gravity="center" android:id="@id/clear_all_button" android:background="@drawable/btn_default_small" android:paddingLeft="0.0px" android:paddingRight="0.0px" android:layout_width="fill_parent" android:layout_height="40.0dip" android:text="@string/status_bar_clear_all_button" style="?android:buttonStyle" />

The difference being the very end: ?android:attr/buttonStyle

Should be: ?android:buttonStyle

This is the line I am now using and it works perfectly!

<TextView android:textSize="@dimen/clear_button_font_size" android:textColor="#ffffffff" android:layout_gravity="center" android:id="@id/clear_all_button" android:background="@drawable/btn_default_small" android:layout_width="fill_parent" android:layout_height="40.0dip" android:text="@string/status_bar_clear_all_button" style="?android:buttonStyle" />

My whole status bar expanded:

<?xml version="1.0" encoding="utf-8"?>
<com.android.systemui.statusbar.ExpandedView android:orientation="horizontal" android:focusable="true" android:descendantFocusability="afterDescendants"
xmlns:android="http://schemas.android.com/apk/res/android">
<LinearLayout android:orientation="vertical" android:layout_width="fill_parent" android:layout_height="wrap_content">
<LinearLayout android:gravity="center_vertical" android:orientation="horizontal" android:background="@drawable/status_bar_header_background" android:paddingRight="@dimen/clear_button_padding_right" android:layout_width="fill_parent" android:layout_height="wrap_content">
<com.android.systemui.statusbar.CarrierLabel android:gravity="center_vertical" android:layout_gravity="center_vertical" android:orientation="vertical" android:id="@id/carrierLabel" android:paddingLeft="5.0dip" android:paddingTop="1.0dip" android:paddingBottom="1.0dip" android:layout_width="0.0dip" android:layout_height="wrap_content" android:layout_weight="1.0">
<com.htc.widget.HtcBlinkingTextView android:textAppearance="?android:textAppearanceLarge" android:textSize="@dimen/status_bar_title_font_size" android:textColor="#ffffffff" android:layout_gravity="center_vertical" android:id="@id/plmnLabel" android:paddingLeft="4.0dip" android:layout_width="wrap_content" android:layout_height="wrap_content" />
<TextView android:textAppearance="?android:textAppearanceLarge" android:textSize="@dimen/status_bar_title_font_size" android:textColor="#ffffffff" android:layout_gravity="center_vertical" android:id="@id/spnLabel" android:paddingLeft="4.0dip" android:layout_width="wrap_content" android:layout_height="wrap_content" />
</com.android.systemui.statusbar.CarrierLabel>
</LinearLayout>
<FrameLayout android:layout_width="fill_parent" android:layout_height="wrap_content" android:layout_weight="1.0">
<ScrollView android:id="@id/scroll" android:fadingEdge="none" android:layout_width="fill_parent" android:layout_height="fill_parent" android:overScrollMode="ifContentScrolls">
<com.android.systemui.statusbar.NotificationLinearLayout android:orientation="vertical" android:id="@id/notificationLinearLayout" android:layout_width="fill_parent" android:layout_height="wrap_content">
<TextView android:textAppearance="@style/TextAppearance.StatusBar.Title" android:id="@id/noNotificationsTitle" android:background="@drawable/title_bar_portrait" android:paddingLeft="14.0px" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/status_bar_no_notifications_title" />
<TextView android:textAppearance="@style/TextAppearance.StatusBar.Title" android:id="@id/ongoingTitle" android:background="@drawable/title_bar_portrait" android:paddingLeft="14.0px" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/status_bar_ongoing_events_title" />
<LinearLayout android:orientation="vertical" android:id="@id/ongoingItems" android:layout_width="fill_parent" android:layout_height="wrap_content" android:drawable="@drawable/list_item_background" />
<TextView android:textAppearance="@style/TextAppearance.StatusBar.Title" android:id="@id/latestTitle" android:background="@drawable/title_bar_portrait" android:paddingLeft="14.0px" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="@string/status_bar_latest_events_title" />
<LinearLayout android:orientation="vertical" android:id="@id/latestItems" android:layout_width="fill_parent" android:layout_height="wrap_content" android:drawable="@drawable/list_item_background" />
<TextView android:textSize="@dimen/clear_button_font_size" android:textColor="#ffffffff" android:layout_gravity="center" android:id="@id/clear_all_button" android:background="@drawable/btn_default_small" android:layout_width="fill_parent" android:layout_height="40.0dip" android:text="@string/status_bar_clear_all_button" style="?android:buttonStyle" />
</com.android.systemui.statusbar.NotificationLinearLayout>
</ScrollView>
<ImageView android:layout_width="fill_parent" android:layout_height="fill_parent" android:src="@drawable/title_bar_shadow" android:scaleType="fitXY" />
</FrameLayout>
</LinearLayout>
<ImageView android:id="@id/tab_divider" android:layout_width="2.0px" android:layout_height="fill_parent" android:src="@drawable/notification_separator" android:scaleType="fitXY" />
</com.android.systemui.statusbar.ExpandedView>

And the images you need to edit for the clear button are status_bar_titlebar_right_rest.9.png and status_bar_titlebar_right_pressed.9.png