From your description I'd venture you had a good group, and while your gear is still a work in progress, I'd imagine you are probably feeling ready to move on to other content. Of course, since you have some Naxx gear, I'm guessing you already have perhaps? :-)
As for over-healing, it is going to be high a lot. Druids do have an insane amount of healing potential. It's not unusual to be on top of the healing charts during a raid and still have 60% overheals. The amount of overhealing you do will be highly fight dependent and variable, of course. Some of this comes from keeping HoTs on targets as insurance. Pre-Hotting allows for the immediate use of swiftmend, and gives you more time to react to a dropping health bar. However it tends to raise the overhealing, and can waste a lot of mana when done unnecessarily.
As for HPS wise there isn't a "magic number" really. Like you said as long as everyone lives, then that's what matters. Your spell power and mp5 numbers should be fine for Naxx.
Other advice:
The Wispcloak (tailoring) is a relatively cheap upgrade cloak-wise. It's not terribly well itemized for a druid, but it can serve you well for a while. Of course, if you have terrible luck in cloak drops (like I have :p) you'll find yourself still doing t9 content with it... I love the off-hand btw. ;-)
You'll want to grab Moonglow and Nature's Splendor from the balance tree. Feel free to drop points from Nautralist and perhaps one from Natural Perfection (or some other place if you prefer), since you really won't be using Healing Touch anymore outside of a Nature's Swiftness Macro.
Swiftmend glyph can be very helpful, as well as the Wild Growth glyph when raiding. However if you prefer the Rebirth glyph, that's fine too. While the rebirth glyph only has situational usefulness, it can save a wipe when used effectively.
You can also read the Druid 202 sticky for more ideas and helpful hints! :D
(Edited my wonderful run-on sentences.)
Edited, Oct 30th 2009 8:49am by someproteinguy
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That monster in the mirror, he just might be you. -Grover