After getting all the standard upgrades and the two new ones already mentioned here, I'm not sure what to do next. I would guess the flashy-dash is a key to access something else, but after combing the levels nothing seems obvious. The only place I can think of that I haven't gone back to is the very beginning, but I don't remember anything special way up there.
You know how stage 5 has that big stretch where you're out of the tank? In that area, if you put something behind blocks the Crusher could get through, you'd only be able to access it once you picked up Wall 1 (which you need to get through the tunnel). Stage 5 was always kind of a dead area, which is a shame because you hardly ever got to use Dive in the original game. But if you wanted to put something between levels 6 and 7, that seems like the easiest ready-made spot.
But seriously, if/when you release a patch, is there any way you could allow a player to toggle the Wall abilities? Once you pick those up, some jumps become a serious pain in the ass.
And since I didn't say it already, thanks for the hack. Any excuse to play Blaster Master again.