I had a chinchilla once. She was extremely cute to look at but my word, she wasn't a low maintenence pet!
They certainly aren't little, docile creatures.... A LOT of exercise needed and they are....FAST! I certainly got some exercise trying to tease her back into the cage.
Plus, the cage they sleep in/live in is usually quite large. If I had one again I would do a lot of planning before hand and make sure I handled him/her from a very early age to get pretty tame. And, with most rodents, they like to chew, anything/everything and yes, the jump VERY high. They can also live for up to 20 years...
I would probably go for a gerbil to be honest and, if I didn't have the cat, would probably get one now