Now that it is all over I will share my tips.
The difficulty of the game seems to ramp up the longer you stay on a dungeon level, but I am truly not sure if it is based on time or rooms visited. It can't be based on treasure because it still ramps up even if you don't collect any.
There are 3 ways to earn points. Collecting treasure, shooting bad guys and a completion bonus for visiting each room
The treasure is a trap. More likely to get you killed than anything else. Collecting treasure takes time, taking more time causes more bad guys to spawn, which makes it harder to make it to the exit. If you drop a bunch of treasure in a room (particularly one past the first level), that room will likely end up with a bunch of bad guys in it (particularly those that track your movement), and you will drain most or all of your lives trying to recover the treasure.
On the first level I don't pick up any treasure on my first life at all. I see no point in doing so, out of 300 games I played I never once cleared the first level without dying. I begin collecting treasure on my second life. I don't revisit rooms I have already been to, I just get the ones that I see. I often complete the first level on my second life, so any treasure I grab there is a bonus.
The thief comes out beginning with level 2, at that point I pretty much stop dealing with treasure altogether, as there is absolutely no way I am going to manage to clear all the rooms on one life, and the thief will have picked most of it up anyway. Shooting the thief when he has a significant amount of treasure is likely to end up with you dying in a fraction of a second (because a bunch of enemies will spawn when he drops his load), even if you don't immediately die the room with the treasure pile will be massively dangerous and more likely to drain away your precious lives than to give you anything that you will actually make it to the exit with.
So with treasure basically eliminated as a scoring mechanism that leaves shooting enemies (which everyone should do) and visiting all the rooms. I visit all the rooms. That gives a 10,000 point bonus multiplied by the dungeon level you are on (not sure how high the max bonus is, there may not be a max bonus, which would explain the twin galaxies high score). Collecting treasure is something you pretty much have to start over on each life, but visited rooms stay visited, thus that bonus can be worked at over a period of more than one life.
I don't always eliminate the corner shooters, particularly those located on the first dungeon level in rooms that I won't be revisiting (those on the outer edge).
Outer edge rooms, particularly corner rooms, are more dangerous as your escape options are limited. I try to visit them first before the dungeon level really starts harassing me.
Now on to the next game. Up 'n Down
http://forum.arcadecontrols.com/index.php?topic=118400.0