Thanks for the responses!
I didn't offer much about my specific needs because I wanted to use a composition (bottom-up) approach to the topic, and I think 'minimum useful base primary' is an interesting question in its own right. I figured 16 would be a popular answer; I started with 15 just to test the envelope. However, I can see lots of other questions arising that are also interesting. For example, I think its interesting that the PHB standard array starts with a 16, and the CB default array starts with an 18.
So to flip the topic completely top-down, why even bother with specific arrays at all? Why not just use point build, and let the chips fall where they may? Well, a few folks here on ENW have mentioned playing or running games where everyone uses the same array. If six players show up for a new game, and all the 22-point-buy character ability scores start with a 20 (post-racial) and end with an 8, how flexible is that really? Are we getting too far into 'false choice' territory? Clearly, not all 22-point arrays are really 'net-equal'. I can personally spend an hour in CB splicing the secondary and tertiary bonuses up six ways from Sunday; sometimes this seems like 'good' difficult decision-making, other times it feels like severe overthink.
One of my challenges with 4E is that I don't get to actually play much (as a player), rather than DM. I don't have the practical experience with character building in 4E that some of you do. But I have played a fair bit of LFR, and I can tell you that when the skill challenges come around, you quickly learn where everyone's dump stats are. Nobody cares you have a 20-whatever primary; they care where you dumped your 8.
I'm guessing some groups choose to use a single array to simply cut to the chase, while also moderating the mini-maxing a bit. The simple scenario I offered in the OP is semi-theoretical; in truth I will probably offer a number of choices to my players, including 22-point-build. But I would also like to reward players for avoiding dump stats. Offering them a package deal of moderate starting array + juicy (house rule) bonus is just one possible way of doing that.
Another would be offering a beefed-up array that could not be bought for 22 points. For example, I might offer a group of players 22-point-knock-yourself-out-buy or an Even Steven 16/15/14/12/12/11 array (28 points). Does anyone think that array would really require rebalacing adventures or monsters? Actually, I think that's a great use for starting arrays in combination with point-buy; getting access to more expensive but less optimal builds.
I enjoy reading how other people have solved ability score arrays for various characters and builds. I wondered what the practical range of scores that folks with more character building chops than I have use. So I appreciate all the suggestions!