Etrecheck says hard drive failing - can I do anything?

Sure it can be fixed, however it's 10+ years old, obsolete and now considered vintage by Apple so it's a prime candidate to be replaced. If you do want to put money into it then use an external SSD as your boot drive. The SSD I'd recommend is the OWC Envoy Pro SX and setting it up is pretty easy if you follow the directions in How to setup an external SSD as your startup disk

By the way, your EtreCheck report indicates a LOT more problems than just a failing HD.

Your welcome, if you are considering replacing it, then I'd STRONGLY recommend getting a Mac mini and add the external display of your choice (personally I like the Samsung external displays) and you will have a far far better system than your current iMac and you would only need to spend about $1500-$1600 . Also, if you decide to go this route and decide to buy direct from Apple, Apple offers 12 month no-interest payments on the purchase assuming you qualify.

Mac Mini's are Macs they work the same as what you own, they just don't come with a display or keyboard and mouse. You can use your old keyboard and mouse and then all you need is the display which only requires a single cable (usually comes with the display) to connect to the computer.