I am TERRIBLE at this game. I tried again last night. 
You are probably beating me........tried a few games then got distracted repairing a pin. Then I ran out of bridge rectifiers last night.....so, will probably try some more this weekend. 
Even if you are terrible, just post them scores!
I finally beat the mech boss on stage 5, but then died immediately on stage 6: 2301780. Afterwards I was so curious about stage 6 that I replayed using multiple credits (that's why this is my 2nd best score). Its insane, you will have to face all previous bosses, multiple at once, possibly on a steep slope!
My current strategy is to finish the first two stages and the desert serpent without using any bombs or lives. Then I choose the bottom path twice, so the boss order becomes:
1- the woman that keeps trying to throw you (anti gravity stage, 2 power ups)
2- the teleportation guy with the mech (sky stage which has 2 power ups and 2 health items!)
3- the dude with the claws (choose the blue sphere for the sky stage!)
It took along time before I could get past the forest stage (before boss 3). On the forest stage I found a path where I only have to touch the ground at the very end. The key to this are the gravity stones (the ones that you can orbit). There are two of these stones in this level and both have a regular jump stone to the upper right. So jump toward the gravity stone to orbit it, then at about 1 o'clock jump to escape the gravity pull, and use the jump stone. If possible you should continuously be using jump stones and keep on kicking, never stop or you will get shot.
After the wolverine wannabe boss, I just bombed my through to the end of stage boss. This gigantic mech takes 3 bombs to take down, that is if you have that many

I only had 2.