Is a mid 2011 imac 27inch worth putting a internal ssd in it ?

I am writing this on a 2011 iMac with a platter drive and 20 gigabytes, works fine for what I use it for...

Light word processing, iTunes, and e-mail....

First, make sure you have a 2011 and not a 2010 model.. Big difference...

Second, you need to make sure you have enough memory,

These models shipped with 4 gig, adding two 8 gig chips helps my iTunes imports a lot....

I have bought from Data Memory Systems for ten years, Other World Computing has memory too..

https://www.datamemorysystems.com/apple-imac-intel-core-i5-quad-core-2-5ghz-21-5-mc309ll/a-mid-2011-memory-upgrades/

https://eshop.macsales.com/shop/memory/iMac/2011/DDR3_21.5_27

You will need an SSD drive, I like Samsung 860 EVO from NewEgg, but they have been replaced with the 870 EVO...

https://www.newegg.com/samsung-1tb-870-evo-series/p/N82E16820147793?Item=N82E16820147793&Description=870%20EVO&cm_re=870_EVO-_-20-147-793-_-Product

You need a temperature sensor, they work for BOTH platter drives and SSD's...

https://eshop.macsales.com/item/OWC/DIDIMACHDD11/

The 2.5 to 3.5 adapter...

https://eshop.macsales.com/item/NewerTech/ADPTADRV/

A tool kit

https://eshop.macsales.com/item/NewerTech/TOOLKIT14/

Last, an external case to put your old hard drive in..

https://www.amazon.com/AmazonBasics-3-5-inches-SATA-Drive-Enclosure/dp/B01MZC303G/ref=sr_1_5?dchild=1&keywords=mazon+Basics+3.5-inches+SATA+HDD+Hard+Drive+Enclosure+-+USB+2.0&qid=1633985836&s=electronics&sr=1-5

I just bought two Crucial MX500 drives and they were very competitively priced. A 1TB was about $100US; don't remember exactly.

If the Mac is operating well and has no problems, I'd say go for it. Even it it were to fail the day after you installed the SSD, the SSD would still be good.

It's a judgement call on your part. I replaced the very slow 1TB HDD in my old 2015 21.5" iMac Retina with a 1TB SSD and it's pleasure to use now.

You will get opinions that vary, my vote is no. A 2011 is outdated and cannot run current versions of Mac OS. It's commercial value is in the $150-200 range, a SSD will run anywhere from $50-200 which would leave you with a machine still worth $150-200.

Probably not.

1. On 10.13 an SSD is only a small incremental improvement over a 7200rpm HDD. Sure system startup is much faster, but a 1-second vs 2-second application opening time doesn't mean that much and once everything is loaded into memory it all runs the same if you have enough memory to avoid swap use.
2. 10.13 only has 2-3 years of typical use life left. Unless you need to replace a failing HDD anyway or plan to keep the 2011 as a dedicated system for running legacy 32-bit mac apps offline an SSD isn't going to provide any life extension.

P.S: If you do upgrade make sure you have a timemachine backup and/or a USB MacOS installer first. Internet recovery is slow and unreliable on 2011s.

Probably not. It is ten years old, and unsupported by either Apple or an Apple Authorized Service Provider, should something break. You can be the most directions-oriented, patient, articulate person and still accidentally damage something inside.

A standard 3.5 in rotational drive shipped with it, and you would need to purchase a 3.5 in to 2.5 in replacement drive adaptor in addition to a new SSD. Although OWC has always sold a thermal cable with 3.5 in rotational drive replacements, so the Mac can regulate the fan based on drive heat, they do not for an SSD (unless they have changed their mind).

It is not easy replacing the drive yourself since these iMacs are difficult to open up. There are several very delicate & fragile connectors that are very hard to see & reach so they can be easily damaged. A 27" LCD Panel is also very easy to damage when handling it due to the huge weight of the panel if it is handled incorrectly (it should never be held flat as the weight will easily crack the panel). You definitely want to review the OWC installation videos first, but those videos make it look easier than what is really is.

https://eshop.macsales.com/shop/ssd/owc/imac-27-inch/2011

Also check the linked OWC page to see if the temperature sensor adapter is required on this iMac when using a third party drive.

This is very true. However, if you're reasonably good working with your hands and following instructions precisely it can be done. You have to be meticulous in following the guides but go slow and double check everything and it's not all that hard.

My reasoning was I was offered $70US for my 2015 Imac as a trade-in. If I completely buggered it up, I wasn't out any appreciable amount of money. However, the reward of having a really great running "new" iMac made it well worth the effort for me.