1993 Mazda MPV transmission repair dilema

I bought a 1993 Mazda MPV 4WD back in '07 for $2,500 and it has been a pretty good and reliable work vehicle ever since, although I've put about $4K in maintenance in repairs into it since, such as replacing the timing belt, water pump, tensioner, a CV shaft, exhaust, one side of engine gaskets, starter motor and even fixing the A/C, plus of course all the scheduled maintenance which was probably somewhat behind when I had bought it. There is some rust on the body, but not critical by any means. Engine was still running well, with the exception of sometimes noisy lifters (since I got it), and the other side needs the gaskets replaced to fix an oil leak.

It’s been a great vehicle for getting around in winter with the 4WD, and good for my work which involves on-site service around central Alberta. I was hoping to get several more years out it with all the money I had put into it to fix it back up, but unfortunately got hit recently with a transmission failure. This was disappointing as I had a transmission cooler installed previously and even had done a trans flush and filter change a year and a bit before, as well as fixed a trans fluid leak. I think it was an internal pump as well as the torque converter, and the transmission shop says it overheated and is in pretty rough shape. They gave an estimate of a good $3,000 to rebuild it, whereas I could probably put in a good rebuilt unit for about $2,000.
Currently I’m driving a car while it is in the shop and I’ve been trying to decide whether to fix it back up again. I’ve been reluctant to walk away from it because of all the money I put into it, expecting most of those repairs to last for a long time, till the van is really worn out.
Anyways, I’m just looking for some advice as to what you think would the best thing to do—to fix this van (has about 271,000K on it, KBB value about $3,500) or else to put that money towards a newer vehicle. Thanks,
Dan