1) If you're only going for the SC goals and not the others, you can tell which ones are SC from the little icon that is displayed for every race on the list. I didn't notice those icons until recently... until like 20 hours into the game.
2) I used a fully upgraded ninja bike and had NO TROUBLE getting all the goals, Well, no trouble.... you just need to learn to race flawlessly, at least almost flawlessly. You don't need any special tricks, you don't even need to be super fast. The only things that cause failure are:
- crashing your vehicle
- missing a turn somewhere
So make sure you avoid those. Collisions with other racers are bad because you will easily exceed the damage allowed.
If you can, use NITROUS. In circuit races use your nitrous in the first lap, it will get refilled completely for the second lap.
Draft behind opponents, if you can. Cheaper than nitrous and as effective.
THERE IS ACTUALLY PLENTY OF TIME, so don't be afraid to slow down when approaching a sharp turn or when there's a lot of traffic.
3) Aiming for the goals will also help you unlock level 3 of all the special abilities.... you can't use them in the goal attack races but racing flawlessly raises their level. I also unlocked the 300 completed races achievement while going for the goals.
4) Someone before me said that going for the goals is time-consuming and frustrating. To tell the truth, I liked the goal attacks better than the career mode. You have a sense of progress, completion, order... you just get rid of goal after goal, you see those you have already completed. Plus no wandering though the city, looking for races or events.