Personally, I don't think it is worth it unless you receive it for free.
It's a 2012 unit, it is five years old which is pretty old for a notebook computer. It has five years of wear on ALL components, but most notably the hard drive (which is probably a conventional rotational model) and the battery. You'd be wise to figure in replacement costs for both in the next couple of years.
I don't know the specs of the particular unit you are considering, but another thing to consider is the LCD backlight. The old cold-cathode fluorescent backlights suffer from the same basic problem with fluorescent lighting technology: fluorescent lights emit less light over time. If this unit uses the old cold-cathode fluorescent backlight, the screen brightness is probably pretty dim, even if you crank it up all the way. When I recycled it in 2014, the screen brightness of my MacBook 2007 was pretty feeble.
LED backlights are more stable over time compared to the older technology. Again, that's another replacement cost that you may wish to factor in if the unit you are considering has the old tech.
If you replace the rotational hard drive with an SSD, it'll be quicker than the day that it was first turned on, but everything else is going to be the same. It likely doesn't have 802.11ac WiFi network and for sure, even with a brand-new battery, it will not have the runtime as a recent system.
In a way, it's like buying an old car. Sure, it'll get you from Point A to Point B today, but how much tread is left of the tires? New battery? Timing chain replacement? New hoses? Brakes? Shocks? Car stereo? It's not going to get better gas mileage than the day it rolled off the manufacturing line.
For sure, I would not look at the purchase price of a 2012 computer as the total cost of ownership over the next three years. Trust me, I've put in plenty of extra dollars into my reliable Mac mini server 2010, but the last modification was 2-3 years ago and it is unlikely that I'd spend another dime on it.
Whether or not it is "worth it" is your call. We all value money differently and personally, I wouldn't do what you are planning on.
Anyhow, good luck with your decision.