To explain on why/when replacement may be necessary, here is my 2 cents:
If the water pump fails, you'll know it. Coolant will get into your crankcase and turn the oil into mud. This is bad, really bad. From the other threads, it seems cost to have this work done is around $2K (plus or minus). If you have to replace the water pump, you may want to replace the primary chain while you are in there. It is only $30-$40 for OEM replacement and although chains do not typically break the way timing belts do, they can stretch over time. Besides, the primary chain has to come off to remove the water pump anyways.
Timing chain issues on this engine seem to be related to it becoming noisy. It is even possible for it jump in extreme circumstances, such as a collision. If it jumps, you may get a P0016 code for crankshaft and camshaft position correlation (P0016 being for bank 1 - the right side of the engine which is closest to the firewall). A noise condition could be due to the chain stretching or the tensioner failing. So if you are in there for any reason (such as water pump replacement), I would say replace the tensioner along with the primary chain, it is a small investment that may save you pain down the road.
VVT Actuators can potentially fail and they may give you the same type of code as a chain that skips, like a P0016 code. Very difficult to diagnose and this is what brought me to opening up my engine. These are a bit pricey (around $100-$150 each and you need one for the right and one for the left). I had the P0016 code which I think was due to the chain, but have read about these failing so I went ahead and replaced both of them. A bigger price investment, but I did not want to have to go back in.
The parts can really start to add up, so you may need to make some decisions on what you want to replace while you are in there. I went the expensive route and just replaced everything within reasonl, including chain guides, valve cover gaskets, and spark plugs.
I'll do a more intensive DIY, but the basics are as follows:
Disconnect battery
Drain Oil (and leave the plug out)
Drain coolant
Remove airbox
Remove intake manifold
Remove valve covers
Remove belts (AC and Power Steering)
Remove power steering pump
Remove engine mount on the passenger frame (be sure to support engine)
Remove crankshaft pulley
Remove bracket that was attached to the engine mount
Remove Serpentine Belt Tensioner
Remove timing cover
That will get you access to all the items of interest (timing chain, water pump, VVT actuators)
From there, you need to be really careful with aligning the crankshaft and camshafts to the proper position, marking the timing chain, locking down the camshafts if you are replacing VVTs, and of course realignment of everything for when the chain goes back on. There will be a big gush of coolant that comes out when you pull the water pump, so be ready for it and use plastic to block of the oil pan from that rush of coolant. Even after draining the coolant from the radiator drain plug there is a lot still sitting in the engine. When I re-filled coolant after the repair it took a little over two gallons to top it off.
I'll include a list of parts and tools used in the DIY, but it wasn't anything too crazy. It can be done without air tools, although air tools always make it a bit easier. I only used my air tools to remove the crankshaft bolt, but there are ways of doing it without it.