Well, being in my mid-30s, I don't feel alienated by the youth-culture look and feel of UA. The last thing I want is for my heroes to look like me! Well, that Mickelthwaite fella looks a bit like me, I guess, but he isn't on every page.
UA is probably the close to the best choice for a d20 Modern FX campaign setting for a couple reasons:
1) Core audience familiarity. As detailed in previous posts.
2) It is generic. Sometimes it is fun to read campaign settings where the world is dominated by insect-like alien shapechangers. Usually these are only fully embraced by a small number of players and the rest either don't buy it or get limited use out of it. By presenting a Generic D&D Fantasy (and I don't think that is an oxymoron) spin on the modern world it can hit all of the familiar highlights and tweak and translate them for use in a modern campaign -- mostly by introducing technology into the conventions.
3) It is broad. Because it covers pretty much the entire gamut of generic modern-fantasy, you can easily define different campaigns by what you exclude, rather than having to add to it. If you want a demon hunting campaign, you can leave out all of the magitech stuff and pick two or three of the organizations that suit the feel that you are going for. If you are going for more of a pulp feel, leave out the magic using advanced classes (mystic, mage, acolyte, etc.) and emphasize the ritual elements of the Incantations. If you want a more Buffyesque feel you add in the Exotic Weapon Master advanced class and mix some Undead in with the Fiends. It is always easier to take things out of a system than to add them, so broad and generic is probably a more functional choice for a stand-alone product than narrow and unique.
As with D&D campaigns, if you want your setting to be really unique you are going to have to do some work yourself because most of the big names (FR, Greyhawk) are generic. Lifting elements from them will only take you so far. I wouldn't expect anything too different from that in a d20 Modern setting.
Cheers