onlky some technical informations:
Your solution might be possible too, but it isn't free and also i doubt that the result is better. Please do try the small imageresizer.exe and do compare it to your solution. I bet it looks not so good, or is harder to edit. Since my way to to dit , does not introduce new colors for upscaling and nearly none for downscaling. ( and it looks really better than nearest neighbour.
Yes did try photoshops filters, they are garbage to be honest.
Potrace from inkscape is not bad, however you have to disable all rounding and error corection filters for small files and it supports only b/w well .And it might be good to use epx3, hqx, eagle or the best till now xbr algorithms for preupscaling.
But thx for the tip. For images there was a good upscaler by akviz ( with good 30 day trial ) .
For downscaling you might also set bg to #ff00ff and use the old rot sprites proggy somewhere in the net (also good for rotating pics nearly without quality loss in any angle , you might compare it to SD icon solution too). also does good 1110% or 120% upscaling: http://info.sonicretro.org/RotSprite