Hi there anotherbottle
I do agree that the inability to set automatic defaults in Publisher ( and most Microsoft applications for that matter ), is a bit frustrating. There is a way to get what you want with one of Publishers built-in features though. It is the "Item from Content Library".
To make this available for all future publications just save these to the default publication which is usually called Publication1.pub . So firstly create a text box and format everything that you want the default settings to be - font, line spacing, margins, alignment etc. You can make the text box any size as you can use the re-size handles to quickly change each new text box to the desired size but initially the new text boxes will be exactly the same size as the sample. Select the sample text box and click Insert> Add to Content Library and a dialog box will appear.
I suggest that you name the item with information in the title so that when you roll the 'mouse-over' it later it will show what it is e.g. Text-Box Arial 10 Centred H&V.
Select a category if you want to but I doubt you should need to unless you are going to have many different formats.
Click OK to save. Now you can insert a 'pre-formatted text box' via the Insert menu ( keyboard shortcut Alt + I then "m" ) or by adding an "Item from Content Library" button to a toolbar that you normally have always visible such as the Formatting toolbar. The Content Library Task-pane should appear from which you can drag-and-drop a new text box to wherever required. You can also pre-format a table the same way. Once you have saved your changes to the publication they should be available to insert from any publication that you open on the same machine. It may take a tiny bit of getting used to but I think that this is the best way to achieve what you are trying to do.
Hope this helps.
Makonz
