Probably hard and expensive, but Canberra really needs just one multipurpose/fit for all sports stadium. Difficult to do I know with both oval and rectangular sports - could you build the seats higher for oval and put seats in front to make it near rectangular? Not sure, but one really good stadium to show off Canberra rather than two half there stadiums would be ideal.
Maybe, but ideally an upgraded Manuka to 20k could also attract some BBL T20 games which makes the upgrade package look quite attractive I would have thought.