They are definitely worth it if you don't have a house with a million elevations. The newest model generation has a lot of features that have matured the Roomba. I could talk about the advanced features for.. well, at least a few paragraphs.
But really the biggest benefits are that (a) it forces you to keep things picked up in order to run it, (b) in the 20-30 minutes it takes you to get out the vacuum, run it, wrap it up, and put it away, you could have gotten 20-30 minutes of other work done, (c) it cleans more thoroughly by cleaning 90% of your floor daily than you attempting to do 100% once every week or two, and (d) it is only like 3" tall and has a side brush which altogether means that it will be able to access a lot more areas than you could with a vacuum (even with a hose).
They say that they'll last 3-5 years being operated daily.
Plus, they are so fun and cute and unpredictable.. something about being autonomous and a little bit random but also methodical. I dunno. I named mine, and consider him my anti-pet; he cleans messes rather than making them! I lubs him! 🙂