Bigger resistors in place of a level shifter on a SD reader?
The main question should be why use the resistors at all, rather than questioning the value change versus voltage.

Years ago I was using a 68HC711 SPI and a long cable run (5 feet). Operating at 5 volts. I was experiencing troubles with errors at a 500 kHz clock rate. I used 470 ohm resistors in SERIES with 3 lines (MISO, MOSI, SCK) also.

I put the resistors in series with the 3 lines because at the data rate I was running, this would reduce any reflections I might have in my pseudo transmission line, without destroying the square wave totally. I discovered this because when oscilloscope was connected that the SPI worked well.

I conclude that the resistors are not used as current limiting, rather they are for noise (reflections) suppression.