I think the AR10 is a superior rifle to the H&K SR9TC.
Here's why:
1)Cost - You can get an AR10 (like the one you have) for under $1300 or an Eagle Arms for <$1000. With ARs, the accuracy is in the barrel. A Krieger? Call it $500. Add a Jewel trigger for $180. We won't include a scope, because that is something needed for whatever you get. So, we are up to $1700 - $2000 for a rifle that will shoot into .25 MOA. How much does that SR9 cost?
2)Accuracy - An AR10 costing less than 2/3 of the SR9 will meet or beat the SR9's accuracy.
3)Action - The AR10 has a nice gas system that can be customized with adjustable gas systems or by moving the gas port if you buy a custom barrel. This action is easy on brass. The action smoothes out and reduces felt recoil. The H&K roller lock action gives an abrupt, jarring recoil in comparison.
4)Reloading - As you pointed out, the SR9 beats brass, the AR10 doesn't. For maximum accuracy you will want to reload. Unless you are a cop testifying in court, you shouldn't use factory ammo due to expense and customizability.
5)Reliability - The AR was tested by NATO and found to be at least equal in reliability to all other systems. I'm not dragging my $2000 rifle through the mud, are you? The rifle is my best friend, Commies and Fuzzy-wuzzies treat their rifles like that, I don't. I wouldn't even treat an AK like that. And I certainly wouldn't treat a $3000 dollar SR9 with a quality European scope like that.
6)Parts - Many AR10 parts are interchangeable with the AR15. Many more are interchangeable with the Knight SR-25. Some are probably interchangeable the the Hesse HAR-10. Isn't someone else supposed to come out with a clone too? I don't worry about parts. Last time I checked match grade H&K parts are expensive. I don't personally know where to get any. (Doesn't mean you can't)
7)Barrel Break-in - This is something that is optional for any rifle, but is also desirable for any accurate rifle.
As you mentioned, the H&K also has ergonomic issues, like the lack of bolt-hold open. I admit I've never owned an SR9, and have only shot the H&K-91. Didn't like it. Plus they are expensive. So I probably won't ever get one either. If I really had a hankering for one I'd get a Cetma or a kit 91. These are much better values and so is the AR10.
If you really want to add the SR9 to your collection, do it. I think it is a fine gun, but there are better out there for far less money. I sure wouldn't sell an AR10 to have one!