I've also been looking for ways to increase the shine in my hair. It's dark brown hair with a liberal amount of gray (mine are quite silvery) mixed in, and it seems like it's been getting duller over the years as the gray has increased, but it's also possible that may not be the cause. I tried Cassia this spring, and while I didn't get the results I was hoping for, it was an enjoyable, spa-like experience. The smell is best described as "grassy" -- I liked it. You do have to rinse repeatedly to get it out, but using a cheap conditioner can help with that. When I researched cassia earlier in the year, I seem to recall reading that not everyone will experience fantastic results the first time out, but if used repeatedly, the shine would increase. I just haven't decided whether I want to order more yet. The Hennaforhair.com site has great info, and there is also a huge thread on the 4a board called Experiences with Henna? you may want to browse through -- there's discussion of cassia included within the thread. The cassia did not cause my grays to yellow at all.
I've had good success now that I've gone back to CG using Aubrey Organics Honeysuckle Rose conditioner and incorporating honey back into my routine, but I have to confess it's only been about a week or so. I also realized I was using way too much conditioner and leaving it in too long, and I think that may have been contributing to the dullness. My hair has gotten so healthy using the methods on this board, and I don't think it needs as much as it did in the beginning. Right now I just let the water soak my hair, give my scalp a good massage (sometimes using a dab of honey while I massage), rinse again, distribute a nickel-sized blob of the AOHR throughout, quickly rinse it out, another quick scalp massage, then I take a dime to nickel-sized blob of honey and distribute it throughout, and rinse. It's easy and cheap and readily available too!