Cap'n Dave...First...I was not looking for a ketch when I found Camaraderie...it just kinda happened when I fell in love with the boat so it is not some sort of "mission" for me to sell others on the benefits of a ketch. I'm more passionate about staysails than mizzens but here are the benefits as I see them of my mizzen.
1. Lowers the needed height of the main mast so I can get under 65' ICW bridges whereas the sloop version of my boat has to go outside no matter what the weather.
2. splits the size of the mainsail so my wife can winch it up and trim manually if the electrics go out
3. if the main shreds...I can still make good way.
4. since mizzen is deck stepped and main is not, I can run my electrical needs up the missen and disconnect easily at deck level when masts need to be pulled. Same advantage can be had with a deck stepped main mast but I kinda like a keel stepped mast.
Kimberlite has the other stuff covered and I've never used a mizzen spinnaker or staysail but if I was heading to the trade winds I imagine I'd get one and it would be a real benefit.
The other thing I like about them is that they are easy to handle and require very little attention so the complexity of sailing doesn't go up.
For a boat of our size, the first two points are very important but I'm not sure how much difference they would make on a mid-40' boat. I would buy a sloop rig again without hesitation on a smaller boat but now I would prefer a ketch rig slightly.