One of the bigger problems in Elite is that you tend to get into a specific rhythm. In part this is because some things just aren't balanced in terms of pay. You might be in a combat ship, but you'll likely never want to take an assassination mission. You'll really really really never want to land on a planet. You might say that there will always be a "best" way to make Credits, but there doesn't have to be! There's actually already a system in game that could encourage variety in game play by injecting some randomness into your activities. Enter: SPAM MAIL.
There's a lot of spam mail in elite currently, people asking you to do largely random missions in silly places that they won't really bother paying you for. This system could easily be changed a bit so that we get them less often and the payout increases greatly. The system couldn't be gamed (you can't cause a mission to be given, and you can't influence what kind of mission it is), but it adds significant incentive to do something different than what you've already been doing, perhaps even to do something you've never done.
Yes, it'd be nice to have the hack and assassination and data courier etc. etc. etc. all perfectly balanced to give you choice, but we could also just make some of these currently annoying spam missions payout 100+ million credits and BAM. Variety. Not the ideal solution, but it should be pretty easy bandaid.