it makes sense to play NV now and if you like it and have time later, then play original FO:3 afterwards. Plus, you may finish NV (depending on how fast or slow you are) only to be greeted by something else: an expansion, FO4, Elder Scrolls 5, and want to play that instead of FO3. To do them chronologically could possibly leave you in a constant state of playing catch up.
You're better off doing them in the original order. The older game is less likely to decline in price further and already comes bundled with all of the DLC (FO3: GOTY). It isn't quite as good, but you get a lot more for your buck. Next year I'm sure you will be able to buy a FO: NV GOTY edition that is a lot cheaper.
Of the games mentioned in this thread, I would rank them like so:
1) ME2. Great combat, good story.
2) FO: NV. Good combat, good story.
3) ME. Okay combat, great story.
4) Bioshock 2. Good combat, okay story.
5) Bioshock 1. Good combat, okay story.
6) FO3. Good combat, one of the worst storylines I have ever encountered.