We barely had any "june bugs" this year but now have a large emergence of beetles that I assume are their distant cousins. They are huge (bigger than the june beetles) and have a coppery-green iridescent coloring. They're so big and lumbering they seem to have a hard time stying aloft.

Do they do as much damage to the lawn as the june beetles do in their larval stage? Anything I should be proactive about for next season?

Actually, I think I just found some info that answers most of my questions.
Doesn't look like they damamge anything since they go for rotten or half-eaten fruit. We have a fig tree that is constantly dropping rotten and damaged fruit.

http://www.sdnhm.org/fieldguide/inverts/coti-mut.html

From early summer through fall, the erratic and clumsy flight of this large green beetle can be seen. Not common 30 years ago, the beetles have since become very abundant, primarily due to the increased popularity of organic gardening. The beetles deposit their eggs during the fall in decaying plant material, especially in manure and backyard compost heaps.

The larval grubs feed on the organic material and develop quickly. Heat given off by the compost allows the grubs to remain active the entire year. When their feeding is disturbed, the grubs roll over on their backs and inch away, using their body segments, not legs, for traction. During the spring, underground chambers are formed by the grubs in which to pupate. Winged adults emerge a few months later.

The figeater can readily eat overripe or bird-damaged figs, peaches, and grapes, but its weak mouthparts are ineffective in ripping open most other plant material. Native plants, including plant pollen and cactus fruit, are rarely damaged initially by the beetles; they usually are found taking advantage of damage done by other insects.

I realize these might be a pest, but I think they are very pretty!

From what I have read, they really don't do a lot of damage; mainly eat rotting fruit. They are really beautiful.