Well hell, why not delete the hit box all together?
Give the player score-checkpoints that they have to achieve in order to continue play, and you just might be onto a great new idea. Have to evolve it some more, though.
Anyway, I think the real "curtain-fire" shmups do get dull after a while, but a lot of the bullet heavy shooters from over the years are fairly moderate. Again, I'd encourage anyone to check out Ketsui. It's not for everyone, but IMO it's Cave's finest, and it fits in the "moderate" category.
Oh, and it's interesting to note that while only some games have a highlighted hitbox, some others that don't still include a ship diagram with the hitbox inside the instruction manual and/or on the arcade cabinet inserts (whatever they're called).
A lot of people have disagreed with me on this, but I still say that Sapphire's hitbox being just slightly on the large side is one of the game's only downfalls. Shrink the hitbox by a pixel on each side (you can increase the enemies to balance the difficulty) and make better (and quieter!) sound effects, and the game would be even more of a legend.