I think these are good ideas, but I wouldn't go too far on any one of them. You want to have your buyers pool remain large. I think you can implement a lot of your ideas without eliminating buyers though.
For green housing, installing water saving fixtures, tankless water heaters, and energy efficient appliances will appeal to many buyers, including more eco-minded buyers, without scaring many off. I think rain barrels would keep some people from buying.
I don't think many banks will consider potential future income from a rental suite to approve a borrower, so the added apartment may not help you that way. It could help get a buyer who likes the idea of owning their own home and a rental to help with their expenses. If you can find a way to add a suite in a way that the owner could use it as their own space and integrate it into the main unit, that may work, but the costs will still likely outweigh the benefits.
Senior housing could be a tough market because if the senior needs assistance, they will likely be searching for a facility that specializes in that, and if they don't need assistance, they probably will not be as hooked by your senior housing benefits. Keeping seniors in mind while deciding what work you do and considering different options to keep your rehabs senior friendly could open up your market to include these buyers, but I am not sure there is enough of a market for them to make it worth it to design your rehab solely for seniors.