I had planned to address someone else's post re: "why pick this over the SGSII?"
And do it in much more detail... but this will have to do as a dry run.

You're responding to a post from 21/06.
"Much" has been ascertained about the hardware since then.
But alas there's still some unclear aspects.

Overall we now know that despite SGSII looking superior in many aspects;
A lot of them will/may end-up being moot...

The only ones that definitely won't be are:
*HDMI
*3-axis Gyroscope
*1GB ROM (Is this right? N9 only has 512MB ROM)

It's not yet clear how the Nokia N9's relatively weak CPU/GPU will manifest itself, if at all.
There'll need to be stress tests (real-world) done on both, to garner anything.
The only obvious area I can think of are games...
But I doubt there'll ever be much of a repository of top-notch commercial games for the N9 anyway.

No SDHC/XC is overcome by the fact that the N9 has great built-in storage (eMMC?) capacity.
That is already cheaper than a similarly sized iPhone4/5 would be.

We know that in actual fact the display overall looks just as good, if not better.
With the only downer being it's 0.4" smaller...

We know the camera's likely to take better quality pictures, & the software likely to be superior.

We know it's likely to take better quality 720p video, & the software likely to be better.
The one downer being it can't take 1080p video.

No MHL/HDMI is addressed by the fact that it's one of the few phones that does 802.11an + DLNA.
This is not a total replacement, but it's does help somewhat.

Then there's feature's N9 has that SGSII doesn't, or has, but doesn't support well 'officially':
*NFC
*BT4 (this is not 100% certain for N9)
*1-1 vid chat (both Jingle & Skype)

One has to remember that developing an entire smartphone OS is huge undertaking.
And one Samsung doesn't have to factor-in to their costs, aside from the UI tweaks they do.

So long as the N9 64GB's only say $50 more on avg...
Then I think a strong case can be made, that it's almost as good value, & certainly as good overall.
So long as the N9 does continue to get decent support after the release.