You'd like to see numbers above 165 , lot of variables.
Were those results from a dry test or wet from oil lubrication of the rings vsit sitting all day and then just tested.
You drop below 140 across the board and it's getting tired.

 

Before the test, I ran the engine for about 30mins in a 10 mile trip to warm up the engine, then I did a dry compression test.

I tested the engine for several reasons like the engine is consuming a lot of oil, the MPG is a bit poor and I had an issue with the spark plugs, they wear out very quickly in just about 6000 miles.

As you say, all cylinders are below 140psi and a lot of variables are involved, but I'm pretty sure that the engine is not in its best days any more, and that makes me think a lot about my possibilities from here.

My mechanic suggested (in his words in spanish) and "engine refresh" rather than an expensive complete overhaul (which is the best option obviously). I was looking for the factory spec psi for the cylinders to see how much down they are, and to see later how close I could get to the factory spec.

 

Since the conditions of the engine is possibly consuming oil, the piston rings are leaking oil into the combustion chamber.

In the 1zz motors 98-2008 here in the states, there are oil passages in the pistons. Not sure if the location of the passages are in the piston ring skirt. These would clog and the repair solution was to drill additional oil passages.

If you add oil to the pistons and the compression rises, then it is piston ring gaps allowing oil to get into the combustion chamber.

 

Yep that is quite low, and would certainly cause poor MPG and oil burning. If you can, test the compression again, but pour a little oil into each cylinder just before testing, about 1/2 a cap of oil (cap of oil bottle). If it goes up, then it’s worn piston rings.
All 4 of my cylinders are between 136-139 dry, but with oil they go up to 190-220, meaning the piston rings are worn. If it does not go up any significant amount, it is most likely leaking valves.
Mine burns roughly 0.5L over 1200kms, or 0.5qt over 750miles.