Got back from my 10,000 LY trip. Made about 30M credits from exploration data.
I generally scanned very little, just scanning unexplored stars and planets that look earthlike/watery/terraformable.
There is now one earthlike planet out there with my name on it.
That 30M got me to allied status with 4 minor factions, which was handy (hint: engineer-unlocking, and creating a new friendly "home" system!)
I returned in solo mode to make sure I avoided any trolls. Some arsehat space-cop still tried to interdict me. I panicked a bit before I realised that I had nothing to hide. Refused to submit anyway (fight the power!)
Exploration is much more profitable since a couple of patches ago, but only earthlike/water/terraformable worlds bring in significant cash. It's not a great way to raise money, but you won't feel like you completely wasted your time.
Scanning some 'unknown' earth/water/terraformables in the bubble might be a good way to make some cash for newbie explorers, but you'd want a cheat sheet of systems to visit - which kinda ruins the whole point of exploration.
Freddie's TIP of the DAY!*
Some people get confused by the approach countdown timer and especially by what the throttle actually represents.
The countdown timer is like a shitty Windows copying wizard and assumes you will continue at your current speed, which is practically impossible since your max frame-shift speed and your acc/deceleration rate is affected by your distance from that target and any nearby gravity wells.
This is why the countdown timer goes much faster than 'realtime' to start with, but can be slower than realtime when you get close on long-range targets (e.g. I've been 10 seconds from Hutton Orbital for over a minute!)
The relationships between speed, acceleration, time and Elite's pseudo-relativistic gravity well mechanics are complicated and non-linear.
The Elite throttle control is not like a car where it represents "what proportion of max power/braking should I apply?".
Instead it's a "what fraction of maximum speed should I be aiming for?"
Your ship will always be accelerate or decelerate at maximum rate in order to reach your target speed. This also applies in normal flight (unless you disable flight-assist) so there's no point hitting full-reverse when trying to stop in a docking bay. It's no faster than zero-throttle.
This is why the 75% throttle at 7s rule works so well and can't be improved with a "0% throttle at 5 seconds" rule. When you switch from 100% to 75% thrust, you'll be braking at your maximum rate, no different to if you selected 0%. And you must start braking somewhere between 6 and 7 seconds away or else your maximum deceleration will not be enough to stop you.
As you get quite close to your target, maximum deceleration becomes "too much" and would cause you to halt before reaching your target. Maintaining 75% of your maximum speed ensures you'll never stop and also never exceed 'overshoot velocity'.
This is why experienced pilots drop the 75% rule after the distance changes from Ls to Mm and try to manually maintain a (faster) speed where their Mm/s = sq-root(distance in Mm).
Note that safe disengage distance (and speed) is >1Mm(/s) for some stations in distant orbits far from planetary gravity wells. However, don't try to go below 6s on a straight-line approach, regardless of the permitted safe speed. Feel free to try as low as 4s on a corkscrewing, gas giant skimming, Buckball rally special though!
*Note: TIP may actually be a tedious and lengthy explanation. No refunds given.
Seriously, it takes a while a get used to the mechancis and the complexity of the game. 
