Personally a cash-out refi could help me get more quickly into all-cash BRRRs or a REI venture in Spain, however I don't know to what extent this is at the expense of rental cash flows, and what is the wiser decision long term.I've combed through posts online and looked for Excel templates to run some calcs and get a sense, but nothing really filled the void... 

The question was - which should someone put money into - this is an unanswerable question because each person's situation is so different and these two products are, as others have said, comparing apples and oranges.  

This may be the case to either leave cash in the deal or if you are unable to cover the payoff of the first mortgage, you may have to sell. 

Currently, I am working on a bachelor's degree for the next few months but after that, I will be jumping into the pool with many of you.

It explains the team that you should develop to have a strong foundation under you while investing remotely.https://www.biggerpockets.com/blog/core-four-real-estate-teamDayton, OH is a market you could look into.

You can't exchange into other foreign countries from a property you own in the US.

What benefit does this provide them?

I currently own one rental property and looking for adding at least one more in 2025.

This 4-bedroom, 1.5-bath brick bungalow is currently tenanted with a long-term tenant of 5+ years, generating $900 per month on a month-to-month lease.

Some of this might be do to seasonality (I don't have anything to compare to because I started marketing on FB about 9 months ago).