Just about everything that was said here is correct, but just to make the facts official for the original questions:
1) No. Despite several instances over the run where a contestant did get a spin or two passed to them in Round 1 after getting 3 Whammies on their own, no one ever actually hit #4.
2) The only one that may have happened, but I haven't seen it myself. Maybe if we get to see the rest of run and the missing episodes one day we'll find out.
3) No. What would be the benefit?
4) No, but it came close in back to back episodes: #499 and the "lost" Back To School episode #500 that never aired in the original run. In both cases, spins were still taken after the 11th Whammy to open up the possibility, but #12 was avoided. (In #499, 1 spin was taken for Mazatlán and then the champ quit, while in #500, both of the remaining spins were taken for Disney World, $1000+ and a sailboat.)
Sidebar on #1: In the time I hosted the game at anime cons, I had 3 separate instances of 3 Whammy passes in Round 1. All managed to avoid elimination, one of them after a record 7 passed spins! And this past summer, I was witness to my friend's run of the game where a player not only got 3 Whammies in the round, but VOLUNTARILY took their last spin!