I had some trouble with the NASCAR Daytona race due to getting spun and losing the draft. The only other NASCAR event that wasn't easy was the "pit-stop challenge." That's the only race I really cheated to win, by getting bumped up to speed. But some say that's easy too.
As much as I hate to admit it, especially to myself, I cheated and got bumped up to 4th place to be able to draft into first for that event too. I just wanted to get it over with.
Could I do it the correct way? Sure. Do I want to? No. I am not a fan of NASCAR. Jeff Gordon's voice annoys the crap out of me. The pit stop at the beginning is a tedious wait if you mess up slightly and have to retry. The NASCAR Special Events are basically scripted events rather than actual races. If you do this, then this, then this, then this, you will win. If you don't do one of those things, forget it.
I didn't mind the A-Spec NASCAR as much because it was more about actual driving than following a pattern, but it was still pattern-ish. I was glad to be done with all of the NASCAR stuff, and move on to fun stuff.
As for the Top Gear Lotus challenge. The best overall advice that I can give you is to ease everything. The Lotus can be a bit "squirrely". Don't turn sharply, don't floor it, don't brake late or stomp on the brakes. Ease into the turns, gently give it gas until full acceleration, brake a little early and don't lock the wheels, especially before/during a turn.
With that said, you do have to bring your skills to that challenge. Just from memory:
I think that I let off the gas just a bit before that first slight turn. I got myself to the left before the turn leading into the tires. If done right, you can pass a couple of cars without being out of control or playing bumper cars. There's a gap, but it takes a bit to thread that needle. Stabilize the car and ease the gas. There's another gap, but it's narrow through the next little turn. You should be able to pass one or two more between the tires. Stay to the right and hug the inside of the turn near the tires in the long turn. You'll pass some more of them. Ease the gas to avoid sliding on the exit into the straightaway. Stay to the right and make sure to brake smoothly and long enough to hug the inside of the turn. You should pass a few more. A slight lift off the accelerator will allow you to take the turn into the next straight. Ease the gas back on though, or you'll lose it. If you ease the turning, rather than sharply or quickly turning, you shouldn't have to slow down for the next turn. Both of these last two are important for carrying the speed. Short brake, ease turning, short brake, gradual acceleration into the short straight, pass on the left, and ease the gas on, waiting until almost straightening the car out for the finish line.
It takes some practice, but it's about not pushing the car too hard, and retaining the speed through the long straights. It's important to carry the speed as much as possible, but those two sections are very important and will allow you to catch the final two cars.
If memory serves correctly, it's a two lap battle, and if done right, it's possible to be in first when crossing the finish line for the first time. That said, it's not important to get there on the first lap. It's only important to be there on the last one.

If any of this seems off, let me know and I'll rerace the event and see if I can give ya better advice. It was fairly tricky for awhile, but I finally managed to get a good handle on it.
I see that I'm not the only person who has had trouble with that Alfa on Eiger. That car doesn't feel natural to me, so I struggled with it. I did one of the Seasonals on that track with lighter, lower HP/PP cars (like the G4) since. I learned that I was taking a couple of the corners completely wrong, especially the last one. I haven't revisited the Alfa challenge since. I really should. It is nice to know that I'm not the only one who struggled to get bronze on it. I should go get gold now.
Edited to add: Quarter, if you're looking for a setup/tune, Adrenaline has every tune on GTPlanet linked on his website:
http://www.adrenatune.com/
They are all listed by car, then by the person who tuned them. You'll be able to find that pretty easily on there.