As an aside, the graphics in Dungeon Ascendance are scaled from 32x32 originals using hq2x and hq3x algorithms. (see
http://www.hiend3d.com/hq2x.html). At IRDC Jeff Lait mentioned that there were decent scaling algos out there for pixel art, so I had a bit of a serach. Jeff also mentioned that 32x32 was big enough to do something with scaling-wise whereas 8x8 really isn't.
Initially I just used a block nearest-neighbour resize from 32x32 to 64x64 and 96x96 which I thought looked better than bilinear or bicubic on pixel art. However, the hqnx really blow those away.
The only issues I had were that some of my GUI icons were 16x16 originally and hqnx occasionally would make circles into polygons etc.
I couldn't find an MIT license hqnx algorithm in Java, so I just prescale the assets when developing and include the scaled-up icons in the game. I have the icons arranged in lines & columns in a big bitmap in 32x32 size. I use an ImageMagick cmd line to split this into individual files, rescale each using hqnx and then use another ImageMagick cmd line to reintegrate the scaled files into a large bitmap. I do this to avoid the scaling algorithm intepolating from the border of one icon into another icon.