I like how current DOE missions have a base completion amount, and an adjusted bonus/penalty amount. I think this would be a great way to start.
If parts are going to be very expensive, then a good base amount is important I think. It's very frustrating for beginners to pull off a win, then have their pp amounts actually subtracted from. I'd like to see newcomers have a chance to become veterans - (insert ominous voice of doom here) the future of this game depends on it.
I'd seen it posted elsewhere that the campaign length has something to do with it too. I am glad to see that things have been refined to the point where it's more cruiser based, instead of the battleships and dreads of old that drove off many who wanted to get into these campaigns. However, if the campaign does not reward pilots in some way, they tend to go elsewhere after becoming too frustrated. I am a coder too, and have worked on game development in the past as a hobby... I can appreciate how hard it is to change settings that really don't show their effects except over time, so I know I'm not asking an easy thing, nor something you haven't all thought of before.
I really like the A-B mission concept, so pilots can choose depending on what they think they can handle. I do think the payouts need tweaking... destroying the entire courier fleet for 180pp, then spending most of it to reoutfit your ship isn't a great way to spend 15-20 minutes.
I am really impressed with the way command variants and carriers were addressed, cost and BPV wise, on DOE. I think this was a great improvement, and gave people a reason to run a NCL+ instead of CLC's all the time (federation example of course). Stroke of genius on the developers' parts...
Maybe by increasing the skill difference between A and B mission variants, and the respective rewards might be the way to go. I know there are problems getting more than two missions to appear without a crash, so working with what is currently viable might be the way to go.
As a side note, the multiplayer stability has been greatly improved, I've had two allies in mission many times with no crashes.
DarkElf's comment on SQL based missions opens huge possibilities as well, with direct access to data variables, our imagination is really our only restraint outside of coding and testing. I'd really like to speak with anyone involved, if there is anything I can do to help with coding or otherwise I'm up for it.
Anyhow, my two cents worth..