It's actually a bit rare for computers to be replaced due to failure.  Most of the time, it's due to obsolescence.  And most of the failure cases that do occur, like yours, are due to some kind of damage.

I have two rules of thumb for replacing computers.  They apply to both desktops and laptops:

1) There is a price to performance curve.  You can get generally get low performance machines quite cheaply.  These are good for email, browsing, etc., but not so much for gaming.  In terms of astronomy, cheap machines are good for image capture, but not so much for processing, with the caveat that if you are doing anything with video (planetary imaging), the performance requirements climb rapidly with larger sensors.  To get the maximum performance, you will spend a whole lot of money.  But the curve is not linear.  There tends to be a place where you can get most of the performance for significantly less cost than the top of the line.  For most uses, I like to shop at the point in the curve where the price just starts to climb rapidly.

2) I start thinking about replacing a machine when the machines in that sweet spot are 4x to 5x faster than the machine that they are replacing.

That is the strategy that I've used for the last 20 years.  I have to admit, though, that it may need some updating.  The reaspon is that computers are getting very, very fast for most tasks.  An older machine that is 4x slower than the current "sweet spot" may still have plenty of horsepower for most tasks.  Now that I am retired, I'm much less likely to replace a computer just because it's old.  Lately, I find that I don't give any thought to replacing a machine that's doing its job well.  Once I notice that a computer needs my attention, that's when I apply the two above rules of thumb.

Specifically for image processing, I'm migrating away from laptops.  Until fairly recently, my most used machine was a Dell XPS 13 with 16GB of RAM, a 1 TB SSD and the fastest Core i7 processor that was offered at the time.  It was running Windows 10.  I used this machine for everything.  At my desk, I docked it so that it had a regular keyboard and mouse, plus 3 monitors.  I recently added a new desktop machine.  It's a Dell OptiPlex 7080, purchased using the above rules for about 30% of the cost of the current top line mini desktops.  It's got one generation back Core i7, 32GB of RAM and a 1TB SSD.  Instead of Windows, I have moved to Linux for my desktop.  This new machine runs PixInsight much more efficiently than the laptop did.  I keep the laptop for exclusively portable use.  I still do image processing on it when I am out at dark sky sites, but the new desktop works much better.

Oh, and I would add that the 1TB drives are too small to be my only storage.  I tend to just keep active projects stored on the SSD's.  I have a NAS at home for long term storage.  It's currently got 12 TB of storage.  When that gets to be insufficient, I'll either upgrade the drives to larger ones, or (more likely) add a second NAS.

-Wade