Have you considered snow and ice load?
Mike

If you mean "snow and ice loads might be an issue with a spreading growth habit" then no, not really miketann. Here in central Maryland, every other house has a JM, dogwood, or redbud with that same upright-but-spreading growth habit. We have a 50-year-old Bloodgood in our yard with the same shape. So snow and ice loads aren't a concern. Thanks!

Well, that's good you don't have to worry about the snow and ice. It's been a problem for me over the years and I have a lot of Japanese Maples. Take a look around my site.
http://i75.photobucket.com/albums/i283/Botann/Winter%202012-13/005.jpg

The Acer shirasawanum, 'Aureum' has poor Fall color. Other than that, it's very nice maple, especially in the Spring.
Mike

What about Ki hachijo, Umegae, Iijima sunago? With some trimming and shaping early on, you could probably accomplish that shape with something like Orange Dream (too sunny?) or Shin deshojo.

Try the Davidsans maple app-- I've plugged in minimum temp, green leaf, upright, and full sun, and these came up. Check his descriptions more closely to see that the form is upright and open, and that the leaves are green enough for you-- seems like there are some options:

http://www.davidsansjapanesemaples.com/japanese-maple-tree-selector/?winter_hardiness=zero&summer_hardiness=full_sun&tree_size=tall&tree_form=upright&leaf_type=&spring_color=&summer_color=greens&fall_color=

Thank you all for the help! Mike, your place is stunning, simply stunning. So beautiful!

Justin, we'll add Golden Full Moon to our list of prospects. Thanks!

Magpiepix, that app is precisely what I needed: thanks! Plenty to look through, including some that we had stumbled upon already, and many more.

I expect to see good fall color on A. shirasawanum 'Aureum' - as with other trees it must vary. The Third Edition of Vertrees, Japanese Maples (2001, Timber Press, Portland) says it's "often spectacular" and can be orange or red, sometimes with some purple.

Unlike with A. shirasawanum a spreading habit is the norm for A. palmatum. But a popular (and therefore apparently easily grown) one that often grows broadly and with a comparatively flat on top is 'Seiryu'. With grafted Japanese maples you can waste a lot of time and money on plants that dwindle away after planting so when a cultivar is a proven performer as this one appears to be that can be a big plus.

I expected good Fall color also, but that was not the case. I traded it to my neighbor so I get to see it in the Fall at his place. Still no good. Spring and Summer just fine though. It's been about ten years now.
Mike

It doesn't offer the intense limey green, nearly chartreuse coloring of the Golden Fullmoon maple referred to above, but A. p. 'Osakazuki' is a good choice. It is a robust, well established cultivar that is widely available in commerce and gets to be a good sized tree in time (20' x 20'). Green leaves in season but absolutely stunning fall color - lots of reds and bronze and orange. Considered by many to offer the best fall color of any JM.

The standard coral bark maple, A. p. 'Sango Kaku', is another possibility. Definitely will offer bright, grass green in-season foliage with some softer apricot-orange fall color. And then that intense red winter branch color. Maybe less of a sure bet regarding robustness, as this selection can present some issues, primarily more of a tendency to develop phytophthora in some climates. But a great tree nonetheless if a healthy clone is selected initially and in proper siting.

Well, we decided on A. palmatum "Glowing Embers". It met all the requirements, and I like the idea of a bit of variation in the fall color. It also has demonstrated heat tolerance, which is something that is an issue (increasingly!) at our place.

Was able to find a selection of them local to us, here--many of them to choose from, too. I felt better choosing a tree that has been growing locally for the past 3-4 years rather than coming on a truck from somewhere else. It's home now, and will be planted in the next week or so.

Thanks for all the help on this!!

Sounds perfect-- I think buying it locally was a very good choice.