re: Would you pay off a 6.5% rental?

I would probably just stay solvent. You can mitigate your 6.5% by parking in a 4% to 5% savings or even 30-day CDs rolled over.

If an investment is funding its own debt service and there is no real money to be squeezed out of that, I would just let it ride. Obviously, if it was 9 or 10, I might think differently.

I mean, $200k cash can reliably bring home over $700 a month in a cash account in the current savings rate environment.

(ETA: You can draw that down while your kids live there, I suppose, but if the asset is staying in the portfolio and go back into service as a revenue generator after the kids are done, I would just keep that note until the end.)