The Dremel gets extensive use in cleaning poorly maintained regs after degreasing and vinegar treatment in the sonicator. I use a variety of brass bristle brushes - round, various cup styles - primarily, fiber bristle brushes for plastic parts, and stainless for the occasional intractable encrustation. I buy the bulk Chinese versions on eBay, as the brushes deform, wear down, and lose bristles pretty readily no matter which you use. That persistant itch on your stomach or side? A launched bristle in your T-shirt. Various bronze "bottle brush" style gun cleaning brushes also can be similarly employed.
I use a corded model - can't recall which, a mainline model - typically on lowest speed.
The Dremel is also good for polishing metal or plastic such as gauge/computer faces, in places hard to reach with a bigger polishing wheel, using the various felt wheels. The cutoff wheels - fiber or mineral - also find regular use in the workshop, though I can't recall many scuba-related needs for such. Ditto for the sanding drums. The abrasive-impregnated rubber polishing tools are a milder alternative to sanding drums, but still fairly aggressive on soft metal. I haven't found any of the grinding accessories - stone, steel, or diamond - to be much good for anything but plastic or non-ferrous metal. They just aren't good quality. I'd say the great disappointment of the Dremel is the generally poor quality of the bits.