I've been ROM hacking in the past for fun and have used the MAME debugger and wla-dx assembler together successfully in Master System, NES and Genesis ROM hacking.
I just recently tried to tackle SNES hacking the same way, starting with Super Mario World (of course). The problem I quickly encountered was that watchpoints do not seem to work reliably. I can set wp:s for some RAM addresses (16-bit addresses ranging from $00 to $1fff) and find routines reading from or writing to them, but for others I had less success.
For example, bytes at $1f17 and $1f19 correspond to Marios map position and they are updated when moving across the map. I set wp:s on these addresses to find routines that update these values, to no avail. Even though RAM clearly changes when moving Mario, the debugger does not break execution. This happens for some other RAM addresses as well. I assume that this is due to some quirk with how the SNES work that I am unfamiliar with. Could someone clue me in as to what happens here, and what I am doing wrong?