Lifespan of 2011 iMac I have a 27&quot; 2011 (i7 3.4ghz 24GB RAM) iMac that I just replaced the drives (1 SSD and 1HDD) in 2 years ago. It runs pretty well now, but is just starting to slow down (and pales in comparison to my 2017 MBP). I'm considering dumping about $400 into it to add an SSD (and run both in RAID0), max out the RAM an replace the thermal sensor. I'm wondering if anyone has done any similar upgrades on a machine with close specs (specifically the age)? If so, did you get the boost in performance you were hoping for or is it just asking too much from a motherboard that old?

**EDIT/UPDATE**
there are some awesome answers/comments/info here - thanks everyone... much appreciated. My main goal is to have 2 high-performing machines. Like i said, I have a 2017 MBP that is great and this iMac is still pretty good for my purposes (no gaming or 3d animation). But once this iMac starts having trouble opening big Photoshop files while I have a bunch of files open elsewhere or performing operations in Illustrator on complex drawings (which I'm just starting to see the beginnings of), it's no longer &quot;high performing&quot;.
I really like the idea of the Mac Mini, but I can't justify the $800-$1000 expense. I could sell the iMac for probably around $500-$600 (and would have no problem justifying the $200-$400 expense), but then I'd either have to buy another large monitor or live with just 2 24-inchers... which would make me sad, I think.
I am convinced that putting the $400 into the iMac is not the best idea. So thanks for helping me get there.
Decisions. Decisions. Gotta mull it over a bit more.
Given you’ve already done the work once, you will be the best to know.

SSD - always a great investment, plus they are almost always fungible - you can put them in newer gear with little to no degradation on speed if they still have life.
RAM - low risk upgrade as well. Especially if you don’t need to max it. Add it only when your benchmarks prove you need it - it’s almost always cheaper to delay buying and only buy when your time to fix the software causing RAM to blow up is worth more to you than the cost of more RAM.

That being said - the $800 Mac Mini will run circles around your 2011 iMac performance-wise. Especially if your software stack can transition to 64 bit speed and run in Catalina. Some old software, when migrated to new Mac hardware simply can not run. New outclasses substantially in every other way including power efficiency, GPU, storage, CPU, memory, expansion.
So for me, the tie breaker is the display - if you love and need it, upgrade or sell to buy a newer but used 27” iMac for value. Also, I have a hunch, a lot of people will want to sell their perfectly good iMacs very soon. This includes Apple if you have cash for new and want to make a deal when the line eventually refreshes. Apple will put machines on the refurbished / clearance rack starting immediately when a new model releases and then again when they claw back all the unsold stock from distributors and retail stores globally. With this bump, I wouldn’t wait and I’d shop to price what you need before next Monday and then have your card ready to buy if you get a short-sale opportunity.
With a Mac this old - there will be a very compelling reason to choose to upgrade, decide trade up to slightly less old or “break the bank” for the latest CPU with a T2 chip. Investing in newer everything can be a great value even if you don’t go new at the $400 range.