I don't really use accessories to change my look, though I do have a nice collection of jewelry and bags (I'm with Angie, footwear is its own thing) along with scarves though I don't wear them often. I use my accessories as accents and completers. They certainly aren't a defining feature of a given "outfit" for me.
Jackets are high impact, but if the jacket has any interesting details then it becomes less useful as an "accessory" to my mind; wearing, say, a bright orange jacket a couple times a week over different tops will be very noticeable compared to, say, a black turtleneck sweater worn with different scarves, but for me neither offers much actual outfit variation. I feel this way about toppers in general though, and I know many don't.
I think it really depends on your personal dressing preferences. Some people like simpler, more basic individual clothing elements so that they can add interest with their accessories; others (like myself) prefer more complex individual items and those become the interest. There's also the idea of how much difference is desired from outfit to outfit. Dressing simply with fun accessories doesn't work for me. I like the clothing to provide the interest and also desire quite a lot of change from outfit to outfit. Finding what works for you is important!