Full-array LED backlighting is definitely better, but also costs more, so it is really a question of whether the extra cost is justified (and different people will have different views on this, depending on their priorities).
And since sometimes the choice is also between different brands, that muddies the decision process further.
Folks who do a lot of watching in darkened rooms will see the most difference/benefit from full-array. On the other hand, some number of those same folks might also decide that plasma was even better in that environment, and therefore head in that direction.
In my case, I have an edge-lit LG 55LW5600, with their version of what I call "pseudo-local" dimming. I can see some modest amount of flashlighting occasionally, when watching in a totally darkened room. Actually, the "worst case" is when there is no content (i.e, while waiting for my BD player to start, or if the cable box is turned off), and the "no signal" screen is being displayed (black background, with a large white time display and a spinning LG logo...). I think this is because local dimming is temporarily turned off, and also possibly because the backlight setting reverts to a high setting when no signal is detected.
But with my current settings, with local dimming enabled, and the backlight turned down a fair amount, the black level performance is quite good when watching actual content.
My set is edge lit from the sides, and so the "pseudo-local" dimming is 8 rows x 2 columns. So the left and right halves of a row are controlled separately. Even with only 16 zones (versus 200 or more for a large full-array set), there is definite visible benefit. It does pretty well with most dark or partly-dark scenes of the actual content. Probably the worst case is having one or two lines of white text (e.g. a movie title screen), on a full black background. The rows having the titles will not be dimmed, whereas the rows above and below will be. So there may be a bit of flashlighting at the ends of those middle rows. Whereas true local dimming would dim all around the titles. In any case, it takes a pretty dark room to see any of this. (As an aside, you might think it makes more sense to edge-light from the top and bottom, as the distance is less. But when the edge-lit sets started to incorporate the pseudo-local dimming, they mostly moved to LEDs on the sides, as having horizontal dimming zones is more effective, in general, than vertical dimming zones. Especially for movies, with horizontal title text, as well as horizontal black bars on the top and bottom. Plus, with more and more HD TV content, the issue of vertical black bars on the sides has largely gone away.)
Paying just $300 more for full-array seems worth it to me. But that assumes that you view everything else about the two sets as equivalent. Within a given company's product line (assuming they make both edge-lit and full array), you might see a larger price difference. In the LG line, I think the step-up to full-array costs more than that, as it also comes with other extras. And in my case, I wanted their passive 3D, and the full-array passive implementation (LW9800 series) isn't out for a couple/few months yet. I think the same situation sort of applies to Vizio, since so far their passive-3D sets are just the edge-lit type, and they haven't propagated the passive approach over to their full-array sets yet. Sony of course is in the active-shutter 3D camp (at least so far), so that applies to all of their sets.
It is true that none of the edge-lit potential problems can be seen in a typical store environment. Not unless the store has a darkened viewing area (like a small, dedicated A/V store).