Worth the upgrade?

Unless the 2017 model has the optional factory solid-state drive ("SSD"—at least 1TB) you will be disappointed with its performance on new macOS versions. Not having the fast SSD is a 100 percent deal-breaker. The standard mech hard drive is far too slow for current OS versions, and the optional Fusion drive, although faster than the mech drive, seems to trigger a lot of trouble reports here.

What macOS version is your current iMac running. Once you leave Mojave 10.14, old apps that are 32-bit will not work and many cannot be upgraded to work on newer OS versions. This free tool will help find if any of your "mission-critical" apps are 32-bit:

https://www.stclairsoft.com/Go64/

Nope, that machine is still based on a HD, it uses a combination small SSD and a HD and they are fused together and this is called a Fusion Drive. Because it has a HD inside I strongly recommend against this configuration too. As Allan mentioned, if you are going to get a used machine please only get one with a 1 TB Apple SSD. If you are determined to buy used also PLEASE only purchase from a reputable reseller such as Macsales.com. Please never buy used from a friend (that is a good way to lose a friend), E-Bay, MarketPlace, Amazon etc.. more often than not these machines are not setup correctly and cause the new owner many problems and are just used, they are not professionally refurbished.

Another option is to buy an Apple authorized refurb directly from Apple. These have ZERO downside, they are identical to new, come with the same 1 year warranty as new, you can buy AppleCare to extend coverage another 2 years, you can finance them interest free for 1 year using your AppleCard, and you can save hundreds of $$$. You can find these at Apple.com then scroll to the bottom of the page and look for the refurbished section. This is by far the best option for buying if you don't want to buy new.

I agree with Jack-19, either get a 24" M1 based iMac or a M1 based Mac Mini. If you decide to go that route, please get one with 16GB of RAM and the largest SSD you can afford. If you cannot afford to pay cash, use the Apple credit card and get 12 months of free financing. If you go with a MM, then you can dictate the display size you get.

I would not recommend buying a 5 year old iMac unless it is well under $500.

if it was me then I would want a bit more than 8GB system mem

and if the hd was ssd then I would go for it, otherwise hd speed would be a limiting factor

Welcome to the Apple Support Communities.

I’d suggest a 24–inch iMac for you: iMac 24-inch - Apple. If you go this route, it is generally recommended that you purchase 16GB of Memory with the largest SSD that you can afford. You can also use Apple Trade-In to get credit towards a new Mac: Apple Trade In - Apple.

Jack

I suppose that would really depend on how much it's going to cost you...

Your welcome.