My 2004 AC has 124000 miles as of yesterday. Standard things have been changed, like timing belt , water pump ETC. Thing is, the original O2 Sensors are still in place and have been with out any codes being thrown. I usually go with the thought , If it isn't broke / don't fix it...But was worndering if this is a wise decision in this case ?

They are a slow wear item, like spark plugs, and their efficiency degrades the same way. The expected life of a 3- or 4-wire heated oxygen sensor is 100,000 miles. It couldn't hurt to replace them and you'll probably see a slight uptick in fuel economy.

The upstream fuel-air sensors are only $55 ea on Amazon. Another $5 buys you the sensor wrench from Harbor Freight. You'll save a least a couple hundred $$$ doing the replacement yourself.