I always looked at the nova bomb as the great equalizer.
Basically a guy gets up there and has 10quint he can't be stopped. Flat out, there is nothing a little guy can do against someone with level 40 planets and a level 40 ship.(haven't played in a bit, so don't know if these numbers are still the same,). But with a 10bil nova bomb, I can still hurt you, and maybe even take a chunk of your money. If you make it so expensive a medium size guy can't afford one, then you take the sport out of it.
I for one hated being nuked. I fought more people and got nuked more times then I could count in a single game. But to be fair when I climbed the ranks, I did more than my fair share of nuking. If it had cost a trillion for nova bombs, I could not have gotten very far.
Random damage sucked when you were trying to whittle away some guy's SD, but I thought it was quite fair. You never knew how much damage was going to be done. Seemed like you had less than a 25 % chance it would even work. But that was the beauty of it. You got a grab bag for a buck. And if you got lucky, you could use it to get even more money. Or if you got lucky/unlucky, you blew up your prize.

so while it is interesting on the levels, I still think the price should be in reach for someone with the money to buy an endevor for even the most devistating nova bomb to keep the big guys on their toes.
If research kicks in and the levels go away, I would like more random damage to come back.

As for backfire damage, well that one is a little tricky. I loved being able to use an endevor or razorback to lob those bombs all day long and only lose 1b for each one that backfired. The problem is that again it only hurts the little guys. Any big guy can afford to buy endevors all day long. Still cheaper than repairing a level 35 voyager.
Why cater to the little guy? Perhapes I have a biased view point. Being one that has been both on the receiving end and the giving end of nova bombs, I think I can say that to be fair, everyone has to have a chance at knocking the big guy down. Without some sort of cheap equalzing device, you cannot have a good conflict. No good battles can be fought when one side always has the big guns. Everyone at the top can sit on their duffs and just do money scrapes all day to stay at the top, without some sort of threat to keep them on their toes. Taking that away from the lower ranked players would make this a farming game, and not a war game as well.

I think Novas Should be (one of) the equalizer for the little guy. Perhaps a cost scale that rises with the player score. I tried the hit and run for twenty minutes in Beta and gave up after killing only 1 million defensive fighters. I could wait til the end of the game to take that sector. I want to play for 10 -15 minutes at a time and enjoy the game- not get tired of it.
I'd also like to see mine disrupters for all those minefields