What is a computer upgrade?

I recently bought some parts off Newegg.com to upgrade my computer.  My question is, when is an upgrade just an upgrade?  Is it just installing a new cpu?  Is it putting simply putting in 2 extra gigabytes of ram.  What?

The problem with upgrading computers is sometimes it turns into a whole new build.  And I think that's what I just ran into.  I wanted a good upgrade to play Left 4 Dead 2 that comes out today.
My current specs are:
AMD Athlon X2 2.6 Ghz
4 GB DDR2 Corsair ram
Geforce 9800 GTX
500 Watt PSU
Windows 7 64-bit professional

CPU upgrade
Compared to the levels in PC Gamer this is a below entry level system.  I was debating on simple upgrades to help push my video card further because I  think currently the cpu is bottle-necking it.  So my first instinct was to simply upgrade the cpu to a higher X2, Phenom, Phenom X3, or Phenom II X4.  I already had my eye on the latter which that cost $175.99.  Total so far $175.99 

Motherboard upgrade
     But before that I had to do some research on my motherboard to see what the cpu list was.  Some of the above was listed so that was good but I did some more surfing to find forums with people who owned the same motherboard.  Some of the above cpus worked but it involved upgrading the bios for the motherboard to read the cpu.  Some people had issues where the higher cpus that the motherboard website clearly said it supported, did not work.

     After reading all the issues that people had, I didn't want to play the guessing game so I decided that I would only upgrade the cpu and motherboard.  But then the issue of DDR2 ram versus DDR3 ram came into play.
     Now it was a quest to search for a motherboard that supported the cpu I wanted and DDR2.  In my find the motherboards that supported the Phenom II X4 cpu I wanted and DDR2, were roughly $50.  Going this route would save me $100 on 4 GB of the DDR3 ram since I'd be using my DDR2 ram.  But then I saw the prices for motherboards supporting my desired cpu and DDR3.  They were $$79.99 and up.  $30 isn't too bad of a price difference to get DDR3 support.  So I opted to get the $80 motherboard supporting my $175.99 cpu.  Total so far is $255.98

RAM upgrade
So since DDR2 ram doesn't work in a DDR3 motherboard, guess what?  That's right, I had to upgrade the ram.  These were $90 to $100 for 4 GB.  I opted for the corsair brand as I've never been let down by them.  They were $94.99.  Total so far in upgrades $350.97.

DVD drive
You must have thought I was done huh?  Well I decided to upgrade the DVD drive because it still uses a bulky and fat IDE cable.  I figure without bulky cables in the case that should help with lowering the heat.  I got an inexpensive Samsung dvd drive for $29.99.  Total so far is $380.96.

Surely I must be done.  I mean a simple idea of upgrading from a cpu that is $175.99 has now turned into an almost $400 upgrade.  I wish the story ends there folks but sadly it does not.

PSU Upgrade
I get all the parts, the cpu, mobo, ram and dvd drive home, uninstall the old stuff, install the new parts, hit the button and....nothing.  No power, somethings not right.  I recheck all the power cables from the psu to the motherboard, and still nothing.  So my first instinct is to assume the motherboard arrived DOA.  But then I see a new power input on the motherboard I've never seen before and my current power supply unit doesn't have that.  Ah, I guess I need a new psu.

But to cover all my bases though, I put in a request to have the cpu and motherboard replaced and I ordered a psu that I saw other customers order with the new motherboard.  The psu cost $109.99.  Total in upgrades is $490.95.

What the crap happened?  I went from wanting just a newer CPU to $490.95 in upgrades.  I hate that but love it at the same time.  Be careful, a simple upgrade can turn into a whole new computer.  This is something that game consoles have over the PC.  Game consoles are usually put out every 5-6 years for $300-$500.  Whereas PC gamers may get the itch to upgrade their PC every year or every other.  But at the same time that's what's so fun about PC's.  Upgrading them to suit your needs, to play a game at higher settings to run smoother or just to keep current with the technology.  Even though my $175.99 turned into a price tag to the tune of almost $500.  I'm happy and will know that this upgrade will suffice for at least three years.

So what do you consider an upgrade?  Do you run into problems like I did and one upgrade turns into upgrading something else?

Coming soon:  My step by step guide to building a computer.