You are absolutely spot on about agp almost = pci. However what about upgradability??? Also pure biz people might even survive with onboard video!!!! Forget fancy video cards!!! Go with onboard video+sound if you REALLY want to save money.
I have min standards for my builds. My builds need to fly thru latest version of an id fps (quake type stuff) and the build needs to have 7.1/optical in/out for sound. Others might be able to cut corners in this dept based on their own personal requirements.
The point of pci-e/new chipsets is the upgrade path. These are not just my words. These are words of the resident authorities on the net. Look around on any good site (few links given earlier). Here's one fresh link:
http://www.tcmagazine.com/articles.php?action=show&id=127&perpage=1&pagenum=14
What if you want to upgrade your gfx or cpu in 2 years?? (Are you going to need extra pci slots or extra pci-e slots in 3 years to add next gen expansion boards???? Hint: Asus Xonar which will allow you to bypass drm and mantain sound quality will come in pci-e form factor)
P.S: Most penryn/am2+ compatible next gen mobos will come with pci-e support not agp, think of it as a free bonus. (p35 comes with pci-e/pci and is my favorite chipset for intel based on what limited reading I have done so far, amd haven't looked into recently as mentioned in my old posts due to my own reasons. i975/i965 can also be used if on a budget but penryn support might be iffy. I haven't investigated onboard video personally because I like to play games so I am not the right person to give advice on chipsets with onboard video)
If you're buying a second hand system or a very cheap system without being concerned about upgradability then AGP is fine (i.e you will go buy an entirely new system in 3-5 years). Just make sure you're saving enough money to justify the lack of upgradability in 3-5 years.
Also if you see an old post of mine you will notice I have posted a damn cheap+nice temp solution mobo for those who need 2gb of ram or less
The asrock dual which supports both agp+pci-e and ddr+ddr2!!!
Only caveat I have never used this manufacturer's stuff before.
Cheers,
Raja