I would echo one question from a previous poster - What do you consider large? The 500 can do larger projects with multiple tenons where added strength is needed. It just isn't suitable for furniture like beds, tables, large outdoor projects (like arbors, pergolas, etc.).
I always look at tools from the standpoint of what they are designed to do. While the 700, with 500 adapters, can do the smaller projects, that is not what it is designed to do. If most of your projects are going to be using 4mm, 5mm, or 6mm Dominos, the 700 would be unwieldy and more difficult to use accurately on the smaller wood parts.
If you are mostly going to use 8mm or 10mm, with some larger (12mm or 14mm), then maybe the 700 with the Seneca adapter may work for you. It's always a dilemma, especially because the Dominos are very expensive. . . . But, regardless, the Domino is worth it. It is probably my favorite tool ever; certainly about the most versatile and easy to use tool in my shop.