I've looked into those recently and decided they just aren't worth the price. By the time you paid for both upgrades you could have purchased a used eMac which would run circles around your upgraded iMac and have a larger monitor to boot! You can purchase a Pioneer Superdrive that is the same model as the MCE for around $60. You could also upgrade your motherboard to a 700MHz G3 for cheap off of ebay. A company used to make a 900MHz G3 upgrade for the slot loaders but it's very hard to find used.
It would be nice if Apple brought back the original design of the iMac with an LCD and low end intel parts and sold it for under $499.