The desktop, which was redesigned and released in 2013 with high-powered components, hasn't been updated since.
While that wasn't necessarily a problem in 20 when the Mac Pro was still among the most powerful desktops on the market, it's been left far behind by Windows-based alternatives that run on the latest and greatest components.
If you own a 2015 i Mac, the answer is more nuanced, but if your machine is pre-2015, get yourself some modern hardware.
The 2017 updates offer displays that are 43 percent brighter and support 1 billion colors—they really were stunning in person. The model names give you a general idea of what you're buying, but getting a thorough answer to the question of worth requires a closer look at the specs from the 20 models.
Additionally, the Apple executives who recently met with Gruber in Cupertino, said that Apple has "great" new i Mac all-in-one desktops in the works.
Some of those i Mac versions will target professional users who need higher-powered components.
Starting with the 2015 i Mac update, Apple solders the RAM to the logic board for the 21.5-inch models, making user RAM upgrades practically impossible (Update: i Fixit has discovered that the RAM and CPU in the 2017 21.5-inch i Mac are once again socketed, making RAM upgrades possible, but difficult and warranty-voiding).