Both are good vehicles, but understand that the fact the 1998 sienna is still running speaks volumes. Also, understand that you're talking about a 20 year old van. The 2004 is 6 years newer,bigger, roomier, even more refined, and will have more safety features to boot. The spoiler was a dealer accessory option; So it's a matter of finding one with that option. I see plenty of both still on the road. Regardless, always have it inspected by a mechanic before buying a used vehicle.