Like I posted earlier, Weird Fantasy comes together as you read the whole friggin' package. The rules themselves work best with the implied low magic / low fantasy setting.
That being said, there is room to tweak, and here are some of my first thoughts on the matter:
Specialists - Sneak Attack - The rules state each "pip" bought in the skill increases the damage multiplier by +1. It also states that putting any points into the skill gives a +2 bonus to the Sneak Attack. I'm leaning towards making that +2 per "pip" bought for the to hit bonus. Only Fighters increase in To Hit Bonus - I'd like to think a sneak attack at a higher level of expertise will actually hit.
Halflings - The implied class for Halflings is Fighter, as the descriptive text refers to "a chiseled, battle-scarred warrior Halfling." I'd rather see him default to a Specialist, but keep the Halfling Expo Advancement, so he will lag behind a Human Specialist.
Fighters - The only class to increase in combat ability. One problem, they may hit more often (if that isn't balanced out by decreasing AC in higher level opponents), but their damage won't be increasing - the Low Magic setting will make magic weapons vey rare - and forget about gauntlets or girdles of strength. My suggestion? Three attacks per two rounds starting at level 6, and two attacks per round at level 11. He still has to hit, but we've increased his damage potential. I foresee extremely long combats at higher levels otherwise.
Clerics and Wizards - On the fence on this one. Thinking of adding one level 1 spell for a +1 in the appropriate stat bonus, a level 2 spell for +2, and a level 3 spell for +3. Clerics aren't going to be going toe to toe in combat anymore, and Wizards are going to suffer from the lack of Christmas Tree goodies. This keeps the player in the game a bit longer before he has an empty spell battery. I don't think the balance issue is all that huge.
Dangerous what a day of driving - with most of that in the passenger seat as my son is getting his "driving time in" - leads one to think of ;)