How about making the cost of acquiring missions higher for high level chars?
It currently costs 1 credit per char level. This means that at the latest, from lvl 40 onwards characters can afford to sit at the terminals rolling as many missions as they need to.
How about sticking some multipliers in there, so that at lvls 20-30 it costs 2 credits per character lvl, lvl's 31-40 4 credits per lvl , 41-50 6 per and so on.. So for example, a lvl 36 character would pay 144 credits per mission rolled, whereas a lvl 44 character would pay 264 credits.
Of course, these values are arbitrary, and should probably be changed to reflect mission rewards, or make them appropriate to cash distribution in the game at the various levels.
Just an idea that struck me as a way in which inflation could start to be combatted
Xlot, rk2.