Your fastest connection to the system bus is going to be through a Thunderbolt enclosure, but you also have to take into consideration the read and write speed limits of the SSD.

In the future, be sure to turn off your computer immediately if it comes in contact with liquid. I stupidly kicked over a glass of water and it poured straight into the back of one of my 2008 aluminum MacBooks, which was closed at the time but woke up when water hit it (apple started glowing). I quickly ripped of the back case and because of the beautiful internals of the unibody generation was able to quickly remove the logic board, drying everything before there was any risk of corrosion. Computer still works fine to this day, three years later. The longer you wait, the worse the damage becomes.

I doubt that; 500GB was probably the biggest drive available at the time that was written. 750GB should be fine, one of my favorite Mac upgrade sites lists that 750GB drive as an option for your exact model.

the $199 replacement fee is an insignificant price to pay compared to how frustrating troubleshooting water damage on an internally delicate machine like the iPhone 4 can be. A ruined antenna would not cause the iPhone to gray out the icons like that, you would just notice diminished function. It's more likely that the chipsets that control those functions are damage.

I'm going to assume this is about a PC, since most Macs don't have spare bays for 3.5" drives, and those that do would most likely see the drive. If it is a PC, then I would check the BIOS settings to make sure that the SATA port that you plugged the drive into is enabled.

when mine did this to me, it turned on once I removed the PRAM battery entirely.

The pre-unibody 15" MacBook pro as well as most of the 15" unibodies were only offered with one resolution, 1440x900. However, the 1920x1200 screen you speak of is an option on most generations of the 17" model. If you had a non high res 17" you would be able to upgrade to a high res screen, but the 15" doesnt have that luxury.

How long before it dies?

There are no 1.67GHz MacBook Pros; the only intel processor in a mac that's slower than 1.83ghz is the 1.66ghz core solo in base model first gen intel mac minis. Very intrigued by this issue. Try different ram and see if the ram is affecting/down clocking the bus maybe? Or maybe you put a 2.0/2.2 generation (macbookpro1,2) logic board in your a1150 (macbookpro1,1) computer?

I've actually seen on a few iPods and one first gen iPhone I have where the USB controller on the board goes out. Only way to fix is a new board in that case.