When I took on the quest to retrieve the platinum chip, I was in quite good repute with the NCR. (I was getting ready to take out Mr. House and thought to deal with the platinum chip first.) Events at the fort turned out to be a blood bath and I ended up killing Caesar. I looted the place clean, destroyed the hidden bunker and made my way to New Vegas to complete the destruction of House. Along the way, I stopped at an outpost with NCR members. I was attacked on sight. My saves all post date the Fort. I'm trying to figure out what went wrong and whether it can be corrected.

I'm inclined to play as chips fall, but I'm also looking at buying up all the expansions and don't know whether the events that unfolded have screwed up the rest of the game.

Anyone have any useful insight?

I do not know. NCR turns hostile if your Legion rep gets too high, if you progress too far in the Legion main quest, or if you shoot their people.

-Nukeknockout

Or if you show up at one of their outposts wearing Legion or Brotherhood armor. I'm willing to bet that the OP is wearing one of the two.

Ah, of course. Forgot that, it's second nature for me to check what I'm wearing before I go anywhere near a faction base. Or just throw all faction armor in the dumpster. Either way, it could also be that.

-Nukeknockout

You got the first part wrong.
Your rep you say is fine, Have you failed Don't Tread On The Bear ? Are you wearing Legion Armour ? Did you kill Boone :shrug:
Thats all I can think of. Killing Legionnaires, tut, tut, shame on you!

I wasn't wearing Legion armor. I did kill Bennie (and Caesar) and took the platinum chip (and destroyed Mr. House's bunker). The "Don't Tread on the Bear" quest is still active. And on the maps, NCR outposts treat me as neutral. But when I show up, all hell breaks loose as they open fire on me.

Unfortunately, I haven't any pre-Fort saves. So, either I play it forward (being an enemy of the people I was trying to help) and hope it doesn't taint the expansions when I order the whole sha-bang in February. Or I restart the game and play through again (in anticipation of February).

Not keen on the latter option.

So your marked as neutral and haven't fail DTOTB yet...
If you go to Camp Searchlight, have you done the quest for the NCR trooper patrolling the place ?
You could go to Camp Forlorn Hope and try http://fallout.wikia.com/wiki/Tags_of_Our_Fallen, give NCR dog tags to the Quartermaster there ?
Also at Forlorn Hope there is a quest http://fallout.wikia.com/wiki/An_Ear_to_the_Ground which you can try?

That is if all NCR are not hostile, give them a shot by first saving and then approaching slowly, maybe sneaking? If they become hostile reload and try fast travelling in ? Just long enough to spark the dialogue and quest then run and do the same when you return.

Otherwise restarting for Febuary is your only option if your dead set on going NCR.