Pimp my 2011 iMac

To start with you can add in a SSD. Here is the IFIXIT guide you'll need to follow: Installing iMac Intel 21.5" EMC 2428 Dual Hard Drive Kit. Once done you can prep it up to be your boot drive and place your apps on it for its speed, leaving your HD in place for your content files (text, images, music, vids, etc...)

Before you migrate your apps over to the SSD you should cleanup the old cache & log files, using an app like this makes quick work of it: DiskDoctor

After you have things setup I would recommend you run Disk Utility to test out your HD once you are booting from the SSD. As well as running a good defrag'ing app on your HD like this one: Drive Genius

Reconfiguring your WiFi & Bluetooth services so you can use Continuity & Hand Off can also be done. You'll need to replace the WiFi adapter and run an extension cable to where the Bluetooth board is (removing it) to the new combo WiFi/Bluetooth board.

I do wonder if its worth it and if all of the possibilities will work here. I would wait until some details on what you are looking for have been proved to work on the older modified systems under MacOS Sierra.