There's more than a few demos that you couldn't run without an accelerator. That was plenty of incentive for me. Also, you do get a real performance boost on other software.
Unless you really want to use an LCD monitor or need to run your screen in a really high resolution interlaced mode, then an Indivision is a nice toy but probably not really crucial. An accelerator will probably give you much more in the way of new things you can do with the Amiga.
