Coming from someone who's studied a bit on HCI, UI Design, and UX...
One of the things that game designers and graphic designers and web designers are taught is that usable space on the display - television, computer screen, handheld, doesn't matter - is a very precious commodity and that it should be used to its fullest but ONLY if it's used well.
Put too many add-ons things there in addition to the 'main screen' and it clutters up the screen and/or takes away from the viewable real estate of the 'main screen'. Put too few things there and you might be making the game and its components inaccessible or accidentally fooling your audience into thinking that the game is missing something.
It can be a touch-and-go thing - no pun intended - as many people will of course have many different opinions on what they like or don't like. But on the whole, there are a few 'guidelines' that are generally followed simply because on a whole in terms of generalizations, some guidelines just seem to work better than the others.
On a PC platform that utilizes a larger single screen and where the game in question isn't like a two-screened game of Tetris, it would make the most sense to make the most of that single screen by using the majority of the real estate to feature the main content and complementing it with a smaller HUD-like add-on or a smaller menu/utilities bar.
In the case of fanbased Pokemon PC games, I would consider everything that is featured in the touchscreen of the DS in the HGSS games to be supplementary and to therefore be something that is readily accessible to the player but not upfront in their face and taking up a lot of real estate akin to a split screen/dual screen.
For example, I would prefer to have a big main screen and the ability to have a thin-ish/short bar along the bottom of the main screen that has a collection of the 'most used utilities' (Pokeradar, check on Pokemon) that could be customizable. This bar could also be docked above the main screen or to the sides. The key thing is is that it would be complementary, useful, and not be huge and in the way and detracting from the main screen.
The only time I can think of where I would want to split my screen in half or something close to half is if I were playing some RPG or something similar that involved me to dress up a very complicated looking avatar. Diablo II would be a good example of a time where a screen splitting sort of thing would be useful if only because you need to see everything.
If there were an option to, oh say dress up a Pokemon with items you have collected (twisted spoons, scarves, braces, etc) like you would dress up your character in Diablo II, then I would say that the dress up screen could definitely be a dual screen/split screen because the Pokemon is just as important as the items that you need to sort through to fit on said Pokemon. Or, if like in Legend of Zelda and the Phantom Hourglass you have the option to draw on a map to mark things, that might suit a larger space simply because of what it is.
But a larger complementary/secondary/split viewing space for no other reason than to simply be there? That just seems a bit like a waste of valuable space to me.
I agree with a lot of points Maruno brought up and I feel that for the most part, the dual screen feature on the HGSS game was something implemented to take advantage of the dual screen rather than implemented as a true necessity. I'm used to the layout of HGSS now but I still feel like the bottom screen is just a bunch of buttons scattered all around ready to be pushed.
What I found useful was being able to pop up my Dowsing Machine (which took up the full bottom touch screen) and what was fun and made sense and was even a little ingenious was using my stylus to dowse while I used the arrow keys to move around. That seemed like a really neat way to truly integrate the abilities of the two different screens and make them equal in importance to each other. I also liked how the Pokedex was implemented as well for similar reasons.
I guess how I feel about it is that I feel that the main menu screen for the bottom screen itself (where all your options buttons are and such) is simply taking advantage of the fact that there is a bottom screen rather than really integrating it into the main screen itself which I felt it could have done better.
Like Maruno said, where it doesn't exactly ruin the experience, it also doesn't add to it and emphasizes that it is all a game rather than an experience. I will reiterate though that when I'm using the Dowsing Machine or viewing the Pokedex, it doesn't feel the same way for the reasons I stated above.
To close my thoughts, I would like to challenge everyone to think about the Wii console and to think about their favorite games for the Wii console and think about how well or how poorly the games utilized the physical full-motion body interactivity ability of the Wii. In relation to that, consider your favorite DS games and see which ones utilized the secondary touch screen the best and why.
Mario and Sonic at the Olympics for the Wii works because you can mime doing all the different Olympic activities. It wouldn't work on a PC because you just lost the primary means of interacting with the game and participating in the game.
HGSS and its split screen works because the platform is that of the DS which is meant to offer different ways of interacting with the game. Specifically, it offers a way to interact with the game using a stylus as opposed to any other method. The Pokeathlon games and the Dowsing Machine are all really great examples of must-use-stylus interactivity. Without these specific features, HGSS in my opinion didn't need to be put on the DS platform.
A Pokemon game could work on the PC because its primary features are still accessible using more typical gaming controls.
The touchscreen IS neat on the DS but only because it can be fully utilized and therefore contribute substance to the game. If I never had to use my stylus for HGSS, then I would say that the secondary touchscreen feature is nothing more than a waste of space and something to look at.
In my opinion, the best thing to do is to make the most of it, no matter WHAT platform you are on and make it make sense. :)
And no, I don't think it is silly at all to do a fan game.
RE: TABLET PCs
For the record, I DO own a Tablet PC (not a graphics tablet but a full tablet PC) which can operate as both a laptop with a full keyboard with a mouse attachment (I hate that little mouse stick in the middle of the keyboard) and a slate-only which means I use the touchscreen screen only (which is also where all my computer's components are tucked away) to write and draw on directly onto it using a special stylus.
I use it in laptop mode when I am browsing the net like this and participating in communities where I am required to type a lot and I use it in slate mode when I am only reading something or doing graphical work. They on-screen keyboard is not an option I like to use at all and all games I play are always played in laptop mode.
If a game required you to be able to switch between two separate places at once, it would be a pain in the butt to do so in slate-only mode because I use the stylus to do everything.
