Do you need military power when using the Rebel Sneak Attack to settle an additional military world?
You still need to have sufficient military power to place the world. Nothing about the placement text implies that ordinary requirements are suspended. Indeed, the game designer says (emphasis mine):


  Yes. And, just like IL doing a normal Settle after a declared
  takeover, the player doing this declares this additional settlement
  during their powers and payment step, discards RSA, pumps Military if
  needed, etc., and then delays the resolution of this additional
  settlement until the pending takeover is resolved. If the declared
  takeover fails, then the RSA additional placement is lost, RSA is
  still used up, etc., with the world itself then being returned to its
  owner's hand.
  
  Exactly the same restrictions as IL after a takeover apply to an RSA
  additional settlement after a takeover, along with the additional
  restrictions noted on the RSA power.


Regarding your Improved Logistics comment: Improved Logistics is a bit of an aberration - it's really, really good. But this card allows takeovers, which is a two card swing (from them to you), which you seem to be discounting. Also, consider that Rebel Sneak Attack would be extremely powerful if it allowed placement of any military world for free (think high value Rebel Homeworld, etc.).