IMac running too hot

Short answer: Those values are okay for a computer that is or has recently been under load.

If you're getting these when it's just sitting idle, something may be wrong. However, if you're getting these while the computer is doing some work (or has recently done some work) these are reasonable. (I have a 22" iMac that I'm comparing yours to)

As for the top of the glass: The (one and only) fan vent is on the back of the computer near the top (where you're putting your hand). It's normal for that area to get very hot, as all the heat the computer generates passes through there. Mine gets hot after a while even if the computer hasn't been working hard.

If you're worried, you can check out the max temperature specs for your components. My iMac has this processor. As you can see under Package Specifications-> Tcase, the maximum temperature it can stand is 72.6* C, comfortably over your CPU's temperature (our models probably have similar maximum temperatures)

90˚c is typical for that system under high load; anything > than 95˚c is when you might want to be concerned. If the CPU gets too hot, or starts to overheat, the system (typically) will clock down the CPU to prevent overheating. The fans shouldn't wear out, so I don't really see any point in trying to replace what's not broken. Intel Mac's run hot, and the fact that the only fan is an output fan doesn't help with heat dissipation.

Something you could do to help alleviate some of the heat is to download smcFanControl (free) and adjust your fans RPM. Instead of the standard 1800 RPM set it at 3500-3600 RPM, which should help cool down the temp possibly 2-10˚c. You might notice more noise from the higher RPM, although you shouldn't worry about it — MacBooks fans generally max out at around 6,000 RPM, and I've cranked one up to 8,700 RPM before.