Should I replace the alternator? ('98 LX)

98 LX470, 140k miles

I was told that I needed to replace my alternator as when the shop turned all the electrical stuff on, the output dipped below where it should be. This was at an independent Toyota/lexus shop.

I then took it to an auto parts store and had them test it. They tested it and it was around 14 volts if I remember correctly (and I was told the machine tests it under load). He said it was on the lower end but still within range so no need to replace it.

Are alternators going out pretty common with these trucks? I'm guessing the shop wants to replace it to be on the safe side because I'm taking it in a long road trip in a few weeks.

There was one time last year when the car turned off by itself in bumper to bumper traffic and the shop said it was the alternator that did that. Hasn't happened since and I have also replaced the battery since then.

Should I replace it? Also, I was quoted about $700 for the replacement, genuine parts and 1yr warranty. This is a fair price right?