Call me crazy, but I think that using the current Amy sprites keep a nice little variation to the NPC characters, as it differs from just being "oh, it's differently colored Amy from that wad" (especially since nearly nobody seems to remember those sprites from back in the 1.09.4 era). Heck, I'd even support using 2.0 Knuckles for these, since he feels more like a different design that could go along the mix. Of course, I'd recommend using more well polished sprites of him.