My vault door was maxed out before the Deathclaw update but now everyone goes through it like the thing is made out of thin cardboard.

If you don't have your defenders in the right spot you are screwed anyway now... so basically the upgrade costs were totally wasted. It also seems the time the attacker stays in the room is related to the number of defenders in the room.... so putting defenders in the vault entrance is a waste of time. You need a 3x room with six defenders to slow down Deathclaws.

You can use 2x defenders to slow down and only sacrifice half your defenders health (it does keep them alive) but you need to keep chipping away at the DC's health that way. I seem to kill all the deathclaws by room 3 that way (although room 3 has 4 defenders in there to delay them... first two rooms weaken the DCs and the last one is the kill room).

But it comes down to the fact that the vault door might as well be left open...

It would say it depends on your strategy, but I'd say no.

I started the game nearly at its release, so my description might not be up to date.

My first room is a generator room, where all 6 dwellers have S/10, L/10 and the best weapons I have.

So raiders never came past this room and none of my dwellers died.

When you are under attack, you cannot rush rooms.

But when the raider try to get through your upgraded vault door, it takes quite a while.

Since they are coming in anyway, I prefer to stop the attack as quickly as possible.

That's why I wouldn't upgrade the door anymore, even if I could easily afford it.

Now since Deathclaws were introduced, my first room has six all-10 dwellers with Lv50 and the door room two of them as well.

Yeah...I've found the delay in raider penetration only prolongs the inevitable now that I have well-prepared dwellers. I'd downgrade the door if I could.

I waited to upgrade my door really late in my vault development (when I was at 190+ dwellers) because I had a ton of caps.

Yes, the maximum improved vault door will delay raiders enough to bring a dweller from 10 floors below. However Deathclaws are much quicker, so make sure your entire first floor has max level dwellers with top range weapons.

...if you prepped for deathclaws then a dely for raiders won't matter. No dont upgrade the stupid door.