Personaly, the differences between simple and complex are more about the execution, and realy shouldn't play in the XP cost, though it would likely have some impact across downtime learning it's not enough to worry about because a longer use of skill has more oppertunity for you to learn something.
The basic and advanced split:
It is likely easier to keep the costs the same (forget using the fast learer xp).
For the Basic skills keep it just that it has to have been (sucessfully?) used since the last developed to increase, forget any tests on it (outside of initially learning it of course), you can always give some a special extra pip if you think a situation has been used significant enough to allow a double advance on a particular skill.
Conversly for advanced have it must be used and insted of using MOS, using a natural roll of 10+ (or TN +1) to advance it a single point (so basically if you have multiple ranks bought in it it wont skip ranks), this keeps it about equivlent to a roll vs the new skill level, without any ancillary/situational bonuses making it allot easier to achieve. This also means you dont have to keep tabs on the 3-6 uses that may span multiple sessions as the skill gets higher.
Alternativly you could use a fail approach, you have to fail a test to advance the skill. This works due to the static TN nature of the skills, and that the more skilled you get the less likely you are to fail normal tasks, while using more complex tasks (ie. penalities) makes it more likely you will learn something new.
At the end of the day what XP you spend on basic skills arent going into advanced skills and what xp your spending on advanced isnt going into basic.
On other bits:
Honestly I dont see much of an advantage to players that spent more on attributes (I may be biased but it took a fair bit of aganosing and geting the midset of the character to decide to have attributes over skills), independantly they do little, they simply reduce the speed at which someone can learn at (they play little part in the actuall skill execution).
However the converse is that the players with higher skills have already learnt more and are far more competent in execution (the making of tests) than those who have the lower skill pool.
In the end as I can see it this appears to balance out, while the high attribute characters will advance faster (likely focusing more on some skills initially), they potentially have less skills as well, so will need to spend more time training (and more time having used existing skills). While those with the lower attributes will progress more slowly and be more diverse as well as having more skills to potentially draw on in some situations so they can actually advance skills that would be less used.
At the end of the day a skill has to have been (successfully?) used.
For example a skill at 1 or 2 may need the higher attribute character to use successfully the skill some 2-6 times to hit the attribute cap, conversly the skill character may only need to use it once or twice to hit the same cap.
