Getpixel() and setpixel() make just one transfer from the LCD, so they are faster than getcolumn() and putcolumn(). Get/setpixel is about 4T, whereas getcolumn/putcolumn are about 240T, where T is about 0.1µS (haven’t measured).
Yeah; the pawn interpreter itself doesn’t take much ram, most goes for program code and data. The freq resp application has 18kB of data, and it also has quite complex graph drawing code (drawing adjustable scales etc.).
Scaling up in X-direction is easy, because you can just call the same putcolumn() for two X-coordinates. Y-direction takes more time, but on the other hand you have to mangle the data anyway to convert 4bit → 16bit. Should be fast enough to redraw display at 25 FPS or more.