To upgrade or replace?

So I have been hand building my own machines for the past 15 years or so. It's time for an upgrade in anticipation of the games I'll be playing over the next 2-3 years (in order of anticipated play time): Guild Wars 2, World of Tanks / Airplanes, Diablo 3, and probably a couple others..

Thing is, my last build went bad early on and the emotional scars have not fully healed. The other thing is, my present machine works well now and most of the parts in it are just fine for carrying forward. But the other other thing is I really don't feel like dealing with assembling a full mobo/cpu/gpu/cooling system upgrade, and also I'm bad at it. I want someone else to do it for me, and do it well.

My current specs are:
Intel Core 2 Quad Q9550 2.83ghz
Intel Stock Fan
4x2gb Corsair DDR3 RAM
2 HDDs totalling 3TB + 120GB SSD
GeForce GTX 480
Corsair 750TX PSU
Cooler Master HAF 932 case

I originally had this big aftermarket fan in there but eventually ripped it out for whatever reason and have just left the stock fan on. It's fine, the CPU doesn't get too hot anymore, as long as I dust regularly. What does get hot is the damn video card. When under load it runs at 95C (apparently normal) and it sounds like a bloody NASA heavy lift rocket is taking off.

What I'd like is a machine that can handle being under full load for long periods of time and do it quietly.

Does liquid cooling make sense here? Maybe some other elaborate scheme? Submerging it in a vat of liquid nitrogen? I am quite out of date in terms of cooling setups.

I'd consider an SLI setup if it's more effective / utilized these days. Also, I like to output to my TV via HDMI for couch gaming.

Also I was one of the 5 or 6 people who actually bought a standalone copy of Windows 7 when it came out and I'd prefer a place that builds systems that don't come with another copy included in the price.

Here's my target machine template:

Approximate Purchase Date: Sooner than later
Budget Range: Looking for parts in the pricing sweet spot, if that concept still applies. Not looking to go super cheap.
System Usage from Most to Least Important: Gaming
Parts Not Required: HDDs, Monitor, peripherals, OS, anything else from above.
Preferred Website(s) for Parts: I usually use Newegg but would like suggestions on other good sites for what I'm trying to do here.
Country: USA
Parts Preferences: Intel CPU, nVidia GPU
Overclocking: Maybe
SLI or Crossfire: Maybe
Monitor Resolution: 1920x1080
Additional Comments: QUIET, people are trying to sleep/think/

Can I get a mobo/cpu/ram/cooling setup pre-assembled so that I just need to wedge it into my case and connect the dots? That I might be alright with.

ETA: If overclocking, what would be ideal is if the builders could do the overclocking themselves and test/optimize it then ship me the OC'd package.

Oh another thing is what should I do with the hardware I'm replacing? I feel so wasteful just throwing it in the closet with the rest of my (typically broken) old hardware. I'm definitely not an ebay/craig's list pro and it feels a bit weird selling off my used equipment. Is that something people do? Everything in the machine right now, works. Historically when I replace parts, it's because they're broken. This'll be the first time in a very long time that I'm replacing perfectly functioning parts simply because they're insufficient.

ETA: Alternatively, I could just buy a completely pre-built system and try to sell my current one complete. Is that a reasonable thing to do?

Thanks for feedback.