I appreciate evryone's help on this. Nice to come back from vacation and find all these IDs waiting :-)

Dates: I used the submission form's instructions of "Date taken, if known" and therefore changed everytime I had a new "photo session". All images, all dates, are the same exact beetle as the one mailed for identification.

My yard is an average suburban grass yard with ornamental plants mixed into the pre-existing pitch pines of the NJ pine barrens. Then a 60 foot stip of native pine/oak woods, then golf course. Are there any other images I can take, or anything I can look at with an 8x jewelers loupe to get to species? Otherwise I'll let it go. Seems to like the sunflower heart.

(well lighted and without loss of resolution) would reveal whether each hind angle area has a distinct oblique depression (A. convexa) or not (A. aenea). If you still have the specimen, you should be able to see these dent-like depressions with 8x magnification. Notice that A. aenea images do not show these dents; also shown there are the more projecting anterior pronotal angles of A. aenea compared to A. convexa images.

This beetle is very tough to photograph. I'm not sure why. I've taken almost a hundred images. Anyway, not in every image, but in many of them there is a consistant "glint" or shadow that would be associated with a diagonal depression in the back corner of the pronotum. You can see a bit of it in the second image, and one I just added.
See the "E" in this graphic http://www.fontriver.com/i/previews/dalek.png, if the 2 outer lines of the "E" are the corner of the pronotum, then the center line is the depression. There is also a sort of depression area in the center making almost a T (or the kanji character for mountain)
Maybe time to let it go.

That observation would be more important to us than showing hard-to-photograph reflective surfaces. However, I believe your images show enough hind angle dent that would satisfy Amara convexa but rule out A. aenea.

I guess it is only a small concern to me, but it is still alive, and I had planned on letting it go when I was done. I didn't want the act of finding out what it is to turn it into a was. I wouldn't feel bad if it died, I just didn't see a point in killing it. So yes (and maybe no) on the dents. The difficulty of working with a tiny live insect is the lack of a handle. After gassing it to sleep I tilt and turn and prop until I "see" the dent, and then a tiny shift and it is all gone. It reflects weird. Sometimes the surface is pitch black and featureless, other times it is a bright featureless glare! But in the pictures and my observations when the dent appears it is always consistant in its placement, direction, and size leading me to believe that it is real. Would I bet money - yes, but not so much that I would mind losing :-)
Tim R. Moyer is a beetle guy in the town next to mine. We've never met, but maybe I'll see if he wants something for his collection. That may "get a handle on it".
I vote Amara convexa.

but don't agree with the choice to (always?) photograph live insects. That's something inherently difficult to do well and is bound to miss important taxonomic detail.

...

which appears next to A. convexa in standard identification keys. Both species occupy open dry grasslands and, yes, A. aenea is reported to frequent "lawns". I favored A. convexa based on the apparent oblique depression near pronotal hind angle (absent in A. aenea) and the relatively convex eyes (flatter in A. aenea). These two species are easy to separate under scope, more difficult with just photos, so Boris might be right in the end.