Stirges are available as a familiar with the Improved Familiar feat if are a 5th-level or higher arcane spellcaster and have neutral as part of your alignment.
According to the SRD entry on
Improved Familiar, "Improved familiars otherwise use the rules for regular familiars, with two exceptions: If the creature’s type is something other than animal, its type does not change; and improved familiars do not gain the ability to speak with other creatures of their kind (although many of them already have the ability to communicate)."
One of the rules about familiars (from the
SRD entry) is that "A familiar also grants special abilities to its master (a sorcerer or wizard), as given on the table below. These special abilities apply only when the master and familiar are within 1 mile of each other."
Improved familiars don't have an entry on the table below, of course, but it seems like there's some justification for giving them a granted special ability. Of the ones you suggested, the +2 to grapple is probably most in line with the powers of the basic familiars; none of them give bonus feats or stat boosts (in 3.5 at least).
Sadly, I didn't cover this issue in
Swarm of Stirges, but there is a spell called "Share Feeding" that lets you temporarily gain half of the Con points drained by your stirge familiar...
(Oh, and a stirge's roll to attach is a touch attack, so yes it could discharge your touch spells in the process).