1-2 Night Trip: Extended Day Hike, or Shortened Week-long?

I use the same gear list for a 1-2 nighter as I use for a week-long trip. It's adjustable to the length of trip. However, my list is pretty well pared-down to the essentials, so I doubt I would leave anything at home using either method you describe. I don't rely much on weather forecasts (with several thousand miles of ocean west of us, our PNW weather forecasters are often surprised). For a short trip, especially a base camp type trip, I may take a heavier but roomier shelter. I also may take fresh food for an overnighter.

Other than shelter, sleeping and cooking gear, the only items I take on an overnighter that I wouldn't take on a day hike are the water filter and an extra pair of socks.

I use the extended dayhike approach for mid-week sub-24 quick backpacks, where planning just takes time away from sneaking out of work.

If it's a weekend overnighter I'm more likely to either have an ambitious agenda which demands better nutrition and a carefully lightened load, or want to bring luxury items (beer, fancy food) and go hang out and fish (for example).

As far as gear goes I take the same stuff I always do. Food is different. I often will take a steak for dinner the first night because usually I get to the TH in the late afternoon and only need to lug the steak for a few miles. I will also pack sandwiches for lunch and maybe even bring a can of beer or 2.

For an overnighter the main change for me is the food and drink. For lunch that first day I also usually bring a hero (haven't heard that term since I moved out west, so thanks for that!) and my dinner will likely not be a freezer bag meal. And I usually bring whiskey or sometimes wine.

If the forecast is good I'll probably leave the rain gear behind as well.

I never really bring luxuries on short outings other than food; like mentioned above, I'll bring some perishable stuff on short outings that aren't suitable to 4 day trips.

I live in Manhattan, and I have no backyard, so I definitely treat most of my overnight trips (which are almost all of my trips) as gear testing outings. I can wear clothing combinations out on walks in all seasons; I can load up a backpack and spend 2hrs strolling through Central Park to test fit and carry; I can try out a new stove in the kitchen; I could spend a night on the floor testing a new sleeping pad; but testing out shelters and sleeping gear in something comparable to real world conditions just isn't possible.

For a 3-season trip in non-bear canister requiring country, my base weight is only in the 6-8lb range, so throwing in a spare shelter to play with, or bringing my Nunatak Arc AT on a 35F night to see if I can push it(with my Specialist as a back-up) is not a big deal.

Heck, I'm going on a 5-night trip to Yosemite/Ansel Adams in 4 days, and I'm probably going to bring both my BPL Nano tarp (primary shelter) and my MLD Spinnaker Solomid(to play with), since bringing the Solomid only brings my base up to 11lbs,(~21lb w/consumables), and I get to test it out in the conditions I'd prefer to be hiking in (vs the East Coast). I may even bring my silnylon Duomid to use in real conditions so I can decide once and for all which Mid I want to keep and which I should sell.

I'm only planning on 15-20 mile days, so the extra pound or two won't be a burden compared to the value gained in refining my gear/skills for the future, and well, playing with gear is fun, and fun is the point of this, anyways.

I tend to load the Sherpas up a little more on a shorter duration trip. Definitely fresh food and a few luxury items like a pillow and a gun.
Just kidding, gun threads are fun, but the pillow is a yes along with a bigger camera.