I've played with spindle drum sanders a few times, and have sleeves and attachments to run a spindle on my drill press. For both rounding off edges, edge profiling in general, or some light curved shaping (saya profiles, for instance), I think they're pretty useful to have available. If you're daring, you can also clamp a straight edge or jig to the table surface and use it as a guide. (this is a bit dangerous though...lose your grip and your piece can shoot out like a baseball in a ball machine.)
Given space and budget, i'd keep a dedicated one around and find ways to use it. The drill press as an alternative, in my experience, isn't an ideal option unless you do some hacking to your set up. Specifically, because the drill press itself isn't designed to take lateral forces against the chuck...so the spindle can wobble a little with use. There's some accuracy/control issues as a result...and also risk of damaging the chuck if you use it this way a lot. The workaround is to put a bearing point under the spindle (veritas makes one at Lee Valley,another called Robosander is more slick and allows you use the sander almost like a pattern trim router bit) ....a second workaround is to build a box top worktable that the spindle recesses into slightly. I've seen these all in action and they do both work well....