'05 Malibu w/100K+ miles. Proactive maintenance?

[MalibuBob]

I've got a '05 Malibu LS Sedan with the 3.5L V6. It's got about 101K miles, on it, the vast majority of which are interstate miles (it's a 90 mile round trip on an interstate to work, 10 days a month). The car is in excellent shape, and the engine and tranny have not given me a lick of trouble. I am very proactive about scheduled maintenance and repairing anything that seems the slightest bit wrong.
Now that it's got over 100K on it, I figure it's time for things to start to wear out. Since I am planning some long trips this spring, summer and fall, I don't want to get stranded somewhere. I figure that the most likely things to fail are the alternator, starter and water pump.
I have been toying with replacing these parts now, BEFORE they go bad, but I'm getting all kinds of opinions on that. Some say I'm just wasting money, since there is no guarantee that anything will fail while on the road. Others say it's a good idea. Just for the record, most of my trips this year will be in the Utah/Arizona/New Mexico/Colorado area, where a breakdown can occur many, many miles from civilization, not just from a repair shop. For what it's worth, I am planning on keeping the car for at least another 50K, although by the end of this year I hope to buy another vehicle for around town, and keep this one as the work commuter.

So... for those of you who may have experience with these things, I have a few questions:

1. Are the items I mentioned (water pump, alternator, starter) the most likely parts to fail now that I'm over 100K? Are there other parts I should consider?
2. Am I saving myself some potential trouble by replacing these parts now, or just throwing money away? Keep in mind that I plan on keeping the car for another couple of years.

Any other thoughts are also appreciated.
Thanks!