I already have silver, and I don't see why a remake is necessary; Gold and Silver improved everything about Pokemon. Each game after that peak sort of took a step sideways rather than forward by adding non-essential stuff and taking out monsters. I can see why you'd want to buy the ruby or the pearl because of the new story and map, but what could be made better in gold or silver?
"If you build it, they will come." If Nintendo releases something with Pokemon in the name, people will buy it, just because it's new. That's the most simple, ignorant, and on-the-surface way to look at the Gold and Silver remakes though.
The graphics are upgraded for one thing. That's definitely the biggest selling point. Remixed music is a huge plus! Add in all the newer Pokemon to my favorite region, a battle frontier, a Pokemon that follows you, some really cool events (http://www.youtube.com/watch?v=VvYjbHv8-4o
) that are easily accessible thanks to wifi, and just tons of other cool new things to discover and I'm sold. Something about taking something with so much nostalgia tied to it and upgrading it and repacking it into something new and awesome is just so very.. awesome!
Another note is that, believe it or not, many people become introduced to Pokemon every day! Plenty of whom have never played Gold, Silver, or Crystal. There are also the younger kids that never were around for the originals. Both groups might be a bit turned off of playing a blocky old game since they don't have any nostalgic feelings for it. Or they might simply lack a method of playing the game.
To put it another way, you would buy a remake of any of the MOTHER games wouldn't you?