in lots of the scenarios with scenic areas i am having trouble keeping people happy. for example i recently did the great wall of china scenario in RC2 and there are a bunch of little "forbidden kingdom" areas that are really pretty. but even though they aren't even that big guests constantly get "lost" in them, get overtired and angry, and wanting to find the park exit. in that scenario you can't let your rating get below 700 and so i was constantly having to open up my guest thoughts button and click all the people thinking "I want to go home" (the #1 most common thought) and manually put them at the park exit to get rid of their unhappy ratings and not lose the whole scenario. i would put food stands and ride entrances and bathrooms at the scenic areas to try and keep the guests happy but it wasn't working. i am really frustrated because i like having the scenic areas in the game for the guests to look at and it seems like a waste to prevent guests from using them. does anybody have any tips that work to keep guests happy in them?

Build a lot of Information Kiosk in those areas. Most people build just one, near the entrance and that's a mistake! You should have more or them, evenly spread all over your park. And remember! It's a unique building that can be accessed from each side so build a path around it to increase its popularity. Kids will ask for directions there and buy maps of your park. It should be more than enough to solve your problem!

It also helps to delete a few pathways if they aren't necessary. If you have big chunks of pathway or long ways with many intersections, try deleting part of them so you only have a few large pathway "circles" (though always only 1 tile wide!) which prevent people from walking the same way again and again aimlessly, as pathfinding AI is really stupid (especially when offered too many options to choose where to go)... ;)

Think as if you're building for the dumb AI of Simcity 2013, only less sophisticatedly bad.

The less offshoots from the path, the better.

There is a known 'pathfinding' bug in RCT2 that causes this, especially in areas with large paved areas. No patch exists to fix it. Only redesigning the paths so that the peeps have less choice of routes will get rid of the problem, if it occurs in a park you design.

As a general rule, remove any excess pathways. Certain Scenarios (Crazy Castle being the best example) i would recommend remowing all offshoots of the main path / paths and sticking to one road, also reading up on the pathfinding AI could help alot

I thought the path finding AI in RCT 2 was improved from the AI used in the original RCT.

It is improved, it's just still bad / weird, at every roadcrossing the AI will randomly cycle the available options, except if the character is trying to leave, and then it will choose one of the two shortest, if i remember correctly.
http://www.rctmart.com/fossil/CrazyCastle1.html has a pretty good introduction to how the pathfinding works.

I think the only improvement was adding some sort of support for wider paths, the basic pathing seems unchanged between 1 and 2.

And this only works while a peep has somewhere he wants to go. Not only leaving, any goal will do, like when they're headed for a ride or food stall. And if not, its not quite random as peeps have a strong preference to walk straight ahead on intersections, not go round corners. This can be used to direct them quite effectively to give them ideas what to ride or buy next. Handymen and other staff who are never headed anywhere, do as badly as rct1 peeps on wider paths, they just don't complain about not getting anywhere. Not sure there is so much randomness at all, the game often doesn't label peeps as "heading to" somewhere even if they are, most obvious with the crowd leaving a ride and many "walking" to the queue to go again. These are easier distracted from their goal than headed ones, but they still have one.

Is the AI about the same in RCT 3?

I have no idea. Bought 3 on the xmas sale here, but started it only a handful of times to check out old coasters, not my taste.

Most likely its totally different, as 3 is a completely new program. From a few mentions of pathfinding I've seen around the web, it has its own set of problems, but don't know specifics. My first impression is a lot less control of peep movement in 3, they have more "personality" and therefore their own ideas what to do and where to go. But thats just a newbie's first look.