For the second one, the caverns...
I deleted the big ferris wheel. Before you do, check it's prestige and make sure it's not already a classic.
If it's new, get rid of it.
The best plan is to place as many rides as fast as you can, so they all become classic about the same time.
The perpetually most poular rides for me were the Zipper, Tilt-a-whirl, the bumper cars, chair swing, and helix (?) that single loop flat ride. The more extreme thrill rides never were profitable for long. You will probably need to keep building other rides, but once they are old, shut them down or get rid of them.
You also need that coaster. Moneys tight though.
Once I got the core "good" rides, and the coaster, I tried to theme as mauch as money would permit, thinking getting the park ratio up would draw more guests. Guess what? It's a waste of time! This scenario is capped at 600 guests!!!! That's what makes it hard, not the ride aging. You can place a ton of rides, but, you spread out those guests and you never make money.
I also only had like 5 food/drink/souvenir stalls. Plus a $1 bathroom, and $1 first aid. If a shop doesn't turn a profit, get rid of it!
Keep as few employees as possible. Keep your rides tight for one mechanic at level 5. Carefully balance your vendors and keep them as low paid and trained as possible. Normal and Low workflow you can pay and train less and they stay happy for longer.
Once you have your coaster, and core good rides, and can maintain a profit and keep 500ish peeps in the park... go to a movie, sweep the house, do laundry, read a book, and let the game run until your first rides are 14-15 years old!
Once they are "reviving" and "classic" you can charge A LOT more! Peeps were happy to pay $28 for the zipper!
I think this scenario needs some more tweaks. I think 800 peep max might have made it go better.
The aging...it needs spread out a little better. They remain old for too long. Revival should last for a few years rather than one or less.
This scenario should have been the last Hardest one.
The last one was really easy, beat in 4 years. The ride aging isn't much of a problem in this scenario. Keep that park ratio up, and you will draw plenty of peeps who will still ride. The rides will still be profitable, even the Hammer Swing.
The caverns with the 600 peep cap? *ugh* Good luck!
I am not sure how I feel about a puzzle that just waiting it out is a valid solution. I enjoyed it though. It was really frustrating. But it was also fun going back to the days where you are waiting to get enough money to build that next section of coaster track.
There are probably other ways to win it. I hope people share their strategy. If you want my park save to look at my craziness, just ask.