I think you nailed the most important tactical issue, namely the dynamic fluidity associated with staggered rather than 'blocked' openings. I suppose skill level is one reason to choose one over the other, but my chess background inclines me to assume the best about my opponent even if I have reason to suspect otherwise.
In the absence of powers you might also just have a style preference, but to me the important strategy is to let the powers dictate your choice of staggered vs. blocked. As I advocated earlier (http://quadradius.com/quadboard/viewtopic.php?t=1776
) picking up the first orb (and other early orbs) can make the decision obvious. Pick up a radial attack power? 'stagger' that guy between two opponent's 4th row pieces. Early jump proof? form as many blocks elsewhere as you can to reduce your opponents opportunities to stall by exchanging and to have his 4th row pieces run away sideways (which would be better for him) rather than backward (which is worse for him).
If I pick up one of what i call 'hoarder' orbs, i.e. orbs that make me want to get the rest of my powers with that guy such as teach, 2x, GQ, others, then I prefer to establish blocks on the front lines rather than staggered formations for two reasons. One is just, again, to buy me more time to pick up powers with that guy rather than having to deal with exchanges he's forcing in the middle. The other is that the blocked formation on the 4th row (say, 3 guys in a row on the 4th row) creates a bigger contiguous space behind them that is easy to maneuver in and can save time picking up orbs.
You all know algebraic chess notation right? Like battleship's grid system? If I have a block of 3 in the first 3 columns, i.e. pieces at A4, B4, and C4...and then two orbs show up on A3 and C3...my GQ/2x/whatever hoarder guy can get one of the orbs, and then the other just two turns later. On the other hand, if I am 'staggered' in these 3 columns, with pieces on A4, B3, and C4...now when the orbs land on A3 and C3, it takes FOUR rather than two turns to get from one orb to the other, since my piece on B3 is in the way. And yes, this does actually come up often enough.
A question to pose: is it any harder or easier to go from a staggered formation to a blocked formation rather than back to a staggered formation? My first guess is its sorta a one way street, that the more blocked you get, the harder it is to get back to staggered, but I'm not sure I can defend that claim...