Hey Steven, thanks for asking about one of my favorite topics - a bit underrated and often overlooked - collars.
I love (and have worn) a lot of different types of shirt collars through the years — button-downs, cutaways, point-spread, even band collars (a go-to in high school) — each has their own purpose. But there's a reason why 75% of our off-the-rack shirts have the exact same Modified Spread Collar: because to me it's the most versatile. A great spread can go black-tie to beach and everywhere in between, and it looks great on just about everyone. So the answer to your question is a big YES. Not all spreads are the same, though. Ours is, again, a modified spread, and it's not i>that wide. It's set at an angle that lands about halfway between a cutaway and a typical points collar. We avoid smaller collars; ours is 8cm (3.14"… hey, pi!) long which is the same as the width of our jacket lapels. And our ties. Harmony...
You know I'm a tie guy all the way, but I'd argue that our spread collar feels as good, sometimes better, without one. It's got enough prominence to stand on its own. (It's also the model for our polo shirt collar.) There's this extra piece of interlining where the collar and the band meet, which gives some extra roll so that it sits above the collar line of a sport coat or something more casual like a military jacket. Even a track jacket. Basically any jacket. It's just nice to see a sliver of that collar from the side profile. So yes, jackets are great, no tie required.
And to your question – yes, sweaters for sure, tie or no tie. V-necks are an easy choice... you can keep the points tucked inside the V for a slightly more pulled-together look, or let it fly outside if you're feeling confident, super 70s, or on drink no. 2 (or all three). A half-zip or track sweater are also fair game, and don't sleep what might be my favorite sweater of all time - the fine-gauge cashmere crewneck. I think it's the perfect marriage of sweater and collar.
Anyway. Don't push your button-downs to the back of the closet. We love those too, buttoned down, or unbuttoned down. They're a big part of the other 25% of our shirt rollup. But we're usually going for simplicity, and the spread is the one that can do it all. Paris TX to Paris France. Always. Give it a try.