I have the orange Cannas.... I don't really mind the caterpillars because I actually planted them to increase my butterfly garden (they are host plants for skippers). However. I get the rust on the leaves which I hate, but I am afraid to to spray because of the caterpillars.... I cut back after a flower has been spent... The oranges ones grow like weeds... I am constantly digging up new ones and donating them to others... I started with one plant and must have over a hundered... I am able to keep them maintained... because they sprout in the same location.... If you want a new planter faster though, bend the spent plant over and let it lay on the ground it will create several new plants.... As you said they get ratty looking, but I keep cutting the older part off and letting the new plant come up... nice fresh looking plant looks great....

I cut mine back when they get ratty too. I have had leaf roller caterpillars for years, but I learned they were skipper larvae, I let them eat away, because the cannas multiply so fast, I knew they weren't going to kill them.