Segagaga is the one box that is worth owning, IMO. De La JSR and SC5 Part 2 only give you a shirt you'll never wear and headphones you'll never use. At least with SGGG you get the awesome pins AND a shirt you'll never wear.
From time to time I'll have an excess of cash that I want to use on a rare item, but I always fall back on a handful of less expensive games or get a rare game that I want to own to play, not collect. Panzer Dragoon Saga, Lack of Love and Cosmic Smash would all get my money before a silver Dreamcast would.
Besides, I have a clear Dreamcast. The best kind of Dreamcast to own: