Am I the only person who likes this movie?

Yes exactly. Borderline sexual assault. Plus, since a rat packer is involved we get the usual depiction of an older woman as a swinish bitch who is beneath contempt. The script even gets her sexy daughter involved in piling on the old lady.
Just watch for the 'hateful old broad' in any movie starring 'Dino' or any of the gang--she's always there.

"my only problem watching it is imagining how much better it would be WITH peter sellers"

I used to feel the same way, but having just rewatched the movie with a lot of distance between my last viewing of it I can say that Ray Walston absolutely killed his part. Knocked it out of the park. On paper it seems like no contest in a Sellers v. Walston bout, but I really love Walston's performance here. Sellers would have played it so differently (offhand, I can't think of a movie where he was anywhere near as manic as Walston was in Kiss Me, Stupid) that the speed of the movie would have been totally changed, and Wilder's tremendous timing is so fast here.

The movie takes a ton of crap, but it's easily the equal of any of Wilder's post-Apartment films - almost all of which are severely underrated. I'd seen it a few times before, but was shocked to find myself really laughing at this today. The construction of the gags, the rhythm of the jokes, the set-ups and pay-offs - for something that aspired to be so baudy it was clasically elegant. And Walston's madcap performance anchors the whole thing. Sellers might have nailed it in his own way - but that might have been the problem, it would have been in his own way. I remember reading that he and Wilder had an acrimonious working relationship anyway, and had it not been cut short by Sellers' health Sellers may have ended up on-screen as being totally independent from the rest of Wilder's finely-oiled machine. Who's to say? But I imagine a tug-of-war between two very different comic sensibilities and tempos.

As it stands, it's a gem in sore need of some legitimate reappraisal.

I thought Novak nailed the sadness and desperation of the character in a way that Monroe couldn't have, simply because she was Marilyn Monroe. Novak really got lost in that character - in a good way, in a way that a star of Monroe's magnitude couldn't have done. The only real "movie star" part in KMS is the Dean Martin role, and that's as it should be. Novak and Felicia Farr are the dual hearts of the movie, and Monroe would have just inherently overshadowed everybody and everything in her path - but for the wrong reasons. Monroe wouldn't have been as believable or as pathetic when the script called for it, or ultimately as sympathetic.

Ugh... no. This was a bad, bad movie in many, many ways.

The central premise is just not funny to me. Songwriting team wants a hit, but can't get one because they suck. So one of the writers decides to get his wife to have sex with a popular singer, then he'll sing their song! Laughing yet? I'm not.

Infidelity is not something I really find all that funny. Of course, the writer hires a prostitute to impersonate his wife, which requires humiliating and kicking the writer's wife out of her own home. Then she winds up in a casino, drunk and alone. Hilarious.

Ray Walston's casting is a problem. For one, he usually played sharp cookies, and having him play a moron wasn't really in his wheelhouse. For another, he honestly isn't good looking enough for the part. The part needed a conventional looking lead at least. Sellers or Tony Curtis, Dick Van Dyke, someone who could convincingly land Felicia Farr. Walston fails that test in spades. I'm wondering what Farr ever saw in this amoral, ugly nitwit. She shouldn't have taken him back.

Dean Martin was an example of overcasting. Way too much. Do I care about Dean Martin getting laid in the early 1960s? Not really. It brings a "punching down" quality to the flick. Martin shouldn't need the help.

Felicia Farr is basically treated like sh*t for most of the movie, it isn't fun.

It's a bad story, miscast and poorly told. Oh, then there's the B&W. Who wants to see Vegas in B&W in 1964? Just makes the movie that much more cheap and tawdry.

This flick is a bomb in every way from beginning to end.