I've got an 8" jointer and wish it were 12". I've got a 15" planer and the only times I wish it were bigger are when I make wide desk tops from 4 boards: I first glue up 2 boards and run them through the planer, then a second set of boards same thing. I then do a single final glue up of the 2 halves and only have to deal with flattening a single seam by hand. If I'm making a 28" wide desk top the 15" planer is barely big enough for this method. A 16" planer would allow me to make a 30" wide panel with a little wiggle room, again using my method of gluing up and thicknessing 2 halves, then doing a final glue up of the halves.
Scott Vroom
I started with absolutely nothing. Now, thanks to years of hard work, careful planning, and perseverance, I find I still have most of it left.