Foam covers over can lights - real difference or just peace of mind?

I did this project two winters ago in a 1970s house with nine recessed lights in the upstairs hallway and bathroom, and I'd say the covers and the caulking are not either-or. My first attempt was just foaming the gap between the housing and the drywall from the attic side, and it helped some but I coud still feel a cold draft on my hand near a couple of the trims in January. The warm air was getting into the housing itself from the room below and riding up through it. So the next fall I went back up, popped fire-rated covers over each one, sealed the edges of the covers with can foam, then blew cellulose right over the top. No draft since.

On the fixtures, I actually swapped three of the oldest ones for LED retrofit units that are rated for insulation contact before covering them. The originals had big old bulbs in them and I did not trust piling anything on top. If your fixtures are the non-rated kind, swapping those first seems smarter than burying them.

As for bills, my gas use went down a bit but we also had a milder winter, so I would not hang my hat on a savings number. The bigger change was the hallway not feeling like a wind tunnel anymore and the dust streaks stopping.

On my place I skipped the covers altogether and swapped the fixtures instead. The house is a 1994 build with six cans between the kitchen and the stairwell, and two of them were the old vented housings that were never meant to touch insulation. Covering those felt like putting a hat on the problem, so I pulled them from the room side and put in new IC-rated LED retrofit housings. No attic crawling required for that part, and the light quality is better than what was up there anyway.

Once the new housings were in, I made one trip upstairs to run a bead of silicone caulk around the drywall cutouts and pushed the blown insulation back over everything. Total attic time was maybe two hours. With a cover setup you're up there wrestling a box over every single can and trying to seal its edges too, which is more fiddly work per fixture. I did compare gas bills, and honestly I can't give you a clean number because the winter after the swap was milder than the one before. What I can say is the cold spot I used to feel standing under the stairwell light is gone, and the dust ghosting on the kitchen ceiling never came back. If your housings are newer and already rated for insulation contact, then sure, covers over the existing cans make sense. But if any of yours are those old vented units like mine were, I'd put the money toward replacements instead of boxes that sit over hardware you don't trust in the first place.

One thing I'd add before you spend the weekend up there: while you're up in the attic anyway, take a good look at where the air is actually moving. In my place the recessed lights were part of the story, but the attic hatch and a couple of top-plate gaps at the exterior walls were letting through just as much, and those cost almost nothing to fix. I used a thin smoke stick on a cold day to trace the drafts rather than guessing. Sealing the big bypasses first made the light covers feel less like the whole job and more like one piece of it.

I have to push back on the idea that you need to replace non-rated fixtures before covering them. That's the whole point of the covers in the first place, they restore the clearance the fixture needs, so a working can that's just old can stay right where it is. I covered four originals in my place three years back and they've been fine since, no tripped thermal protectors, no burnt smell, nothing. Swapping housings is a fine upgrade if you want new LEDs anyway, but telling someone to rip out working fixtures first turns a Saturday job into a way bigger one. If the fixture works and the cover goes over it, you're done.

Reading this as someone who has zero attic expirience, so forgive me if it's obvious. How do you even tell if your fixtures are the safe-to-bury kind or not? Mine are from when we bought the house and there's no label I could see without sticking my head up there. Also wondering if those covers are one size fits all, because my lights look like diffrent sizes from below, one big one in the kitchen and smaller ones in the hall.

First time posting here so hope this fits the thread. My situation is close to the OP's but my kitchen cans are on a dimmer, and the bulbs run pretty warm. Reading about snapping a box over each one and sealing it up has me wondering if that just bakes the fixture all summer with nowhere for heat to go. Has anyone with dimmed lights done the covers and noticed bulbs burning out faster, or the trim ring getting discolored? I don't want to trade a draft for a cooked fixture, but maybe I'm overthinking it.

Update: went with the combo approach one poster described, foamed the housing gaps then snapped covers over each can and piled the insulation back. Dust streaks stopped, so that part seems solved. But the attic hatch is clearly the bigger leaker now, you can feel cold air pouring down the ladder. Anyone have a cheap weatherstripping setup that actually holds up?