Even thinking about converting your sailboat from a ketch to a sloop, while surrounded with ketch owners can be a dangerous activity. I cast no aspersions on ketches in general and my thoughts about converting TIH are governed by my planned use of the boat. From my research on the subject the benefits of a ketch rig are as follows;
1. More manageable sail size split between both masts.
2. Heavy weather option of Jib and mizzen.
3. Redundancy in the event of loss of rig (assuming they are not connected by a triatic stay).
4. Place to hang radar and/or wind gen.
5. Nice on a reach.
6. Permits the use of a stay sail between masts.
The drawbacks are;
1. More complicated rig.
2. Will not go to weather as well as a sloop.
3. Mizzen doesn't work well on a run.
4. More expensive (mizzen sail costs $1,500 approx).
5. Interferes with wind vane.
6. The mizzen makes it difficult to mount solar panels / install dinghy davits etc. aft.
Specifically on my Whitby 42
1. The stays are pretty close together requiring running back stays on the mizzen and the use of a triatic stay. At least two W42 have lost their mizzens and I believe that I would have to install a beefed up compression post under the mizzen mast.
2. The main boom is the old style tube type (designed for rolling reefing) which I would have to replace as I want to use slab reefing. This will permit me to increase the main boom length from 14.5ft to 18ft.
3. I will be installing wind vane steering and the mizzen would complicate this.
4. I am a huge believer in a dinghy arch which incorporates a mount for solar panels etc.