Replacing engine in 2007 Mazda 6 - thoughts?

So, we've got a 2007 Mazda 6 (2.3 fwd) which my wife has had as her primary car since buying it used as the second owner. We have taken care of the car pretty well and have not had too many major issues. A week or so ago, at around 160,000 miles we had an unfortunate engine failure. The shop said that something let go in the bottom end and that it was toast. So, we bought ourselves a new 2016.5 CX-5 GT AWD as a replacement since she was ready to trade hers in at the time. They weren't offering much of anything for a trade-in for a car with a blown engine so now I've got a spare 2007 mazda 6 and I'm trying to determine it's fate. It has been an excellent car to us and it would be nice to have a second car to have around (my other car is not a daily driver).
I have received quotes for 3900-4200 for an engine replacement for a used engine with 83,000 on it (w/ 1 year warranty). What do you think, would you do it? I am leaning towards going for it, there doesn't seem to be many other cars in the price range as nice as the 6 and they are all over 100-140,000 miles. I think she has some life left in her but I'm not sure of the other parts failures around this mileage (160,000). I do not need the car for my commute, as I take the train which is in walking distance so it's really just a backup car.

Thanks for any insight. I'm trying to make the decision by Monday.

Sorry about your motor...I do not think the car is worth another $4k investment if it is an extra car.

In my area of California, a clean with no rust Mazda6 160k miles I see several in my area same year $3500-5000.

If it is clean and no rust, might be better to sell it as a mechanic special and walk away with $800-1200 in your pocket.