The XMLUpdater properties page doesn't expand vertically past the size where 5 rows are visible in the 'Updates' pane. It should stretch as far as I want it to.
The updates soon get unwieldy even so. I should be able to create and name tabs in the 'Updates' pane that collect my updates into related groups (I currently have to have a separate XMLUpdater transformer for each set of update operations so I can organise them into self-documenting functional groups).