Games in lores would probably look fairly "blocky", so that kind of filter (at least on the X-axis) may indeed increase the gaming experience. For the Y-axis, we already have the scanline emulation, which seems to be quite popular (we get lots of eMails about that!). So yes, we'll think about an additional mode like that.
As for Graffiti, it's advantage under AGA is that the 256-colour hires screen is generated by a 16-colour S-Hires screen, which only uses 4 DMA slots, thus leaving the full 7MB/s access speed to chipmem. I doubt that a WB emulation using this mode is possible, but existing software like the Shapeshifter driver comes in handy.