As an injury prone runner I like to switch out one of my runs a week for a low impact form of cardio. I'm aware that you'd need to spend more time crosstraining than running to get the same cardiovascular training effect, but how much more?
For example is 30 mins easy running "equal" to 1 hour on the elliptical or 1 hour cycling? Is the elliptical better than cycling since it mimics running form more?
You could look at caloric expenditure and equal them out. But can replacing a run with a swim improve your performance, that is debatable aside from if you are injured you cannot performance well.
Do both, especially if you can only do 30 minutes of running a day. Also try slowing down your easy runs. A lot of people who say they are injury prone just don't take their easy runs slow enough.
Yes, elliptical works. I use it often in winter when it is too slippery or/and cold to run. Just adjust the level of resistance properly. As for coefficient, 1.5 is definitely more than enough. I.e. 45 min vs 30 is OK.
Assuming you can still run many days of the week, I'd argue the 60min of cross training would be better overall if at roughly the same intensity.