IMO Panama is important... if you can hold it (we cannot). With the Canal secured, the US Navy would be restricted to the East Coast, which means that we could roam free in the Pacific and we would know with 100% certainty that the US Navy could only come to the Pacific through the southern part of South America. We could establish a blockade and it would take a long time for the US AI to regain momentum, if they would be able to achieve this at all.
Out of interest, how would this be (in game) different to just putting a fleet outside of Panama?