Once you upgrade your jump skill to the maximum it got annoying to jump past and over platforms; maybe you could incorporate a Mighty Bomb Jack (NES title) style mid-air stop? Either that or have your jump increase as you hold the jump button.
If you wanted to add a little structure to the system, perhaps you could start in a lower corner of the world and try to reach the opposite top corner? Spelunky was structured so that you wanted to reach the bottom of the screen, and it seems your upgrades here are tailored to going upwards. You could also have it so that you generate more pits as you progress upwards, to increase the difficulty.
This is a neat diversion as it stands.
Yeah, jumping is crappy as hell, I have to think of something, and mario style hold-it-longer seems alright. Actually I was just lazy not doing that
I actually never played spelunky (i probably shouldn't be saying this here), but if you played a little longer you'd notice, that you have to go back up after you go down, and after that you have to wander about some more. I made going down first, since it's easier, and also the levels are generated to facilitate current direction. It is pretty hard already to go up, since you can fall 4 floor in 3 seconds.
And upgrades are upwise to reduce dead-end situation probability.
Thanks for critical response, I will try to polish it considering to your remarks.