Usually a dealer will give you a decent price on your trade in order to make the deal for the new one. smart doesn't have to do that, and I don't think that anyone should consider trading when buying the smart as the dealer has no incentive to take your trade.
One thing you must always consider when buying a vehicle is what resale is. Even if you plan on paying it off and are not concerned about resale generally speaking, you have to think about what would happen if the vehicle is totalled, or you lose your ability to work and must sell, or whatever. It is unfortunate that your Hyundai has low resale, but there are many other forces at work here too, a tumbling economy, a serious drop in all auto sales, and your Hyundai is a big fuel consumer at a time when fuel prices are so high. These might all be reasons for it's low resale too. I would try to sell it to a private party rather than trade if they are trying to get it at such a low price. Out here in Arizona, typically, even before the economy got so bad, the most you could expect to get for a used vehicle is wholesale, or trade in value, never retail. If you can get wholesale from a private party now, you would be doing good. I don't know what its like where you live, but the market is getting flooded with used SUV's that don't sell, and yours is so new, your still not leveled out after the initial depreciation hit. Good Luck, and hope you can sell it soon.