Hi William -

Just some experience based thoughts on your inquiry.  As Earl mentioned, he
and I have been around the horn on these issues more than once:

Solder filled vias tend to do everything but what one really wants them to do.
 One thing is to steal solder from the primary solder connection, when they
are located in the pad, as you have noted.  The other is to create a series of
irregular sized solder globules on the opposite side of the board, which can
get real messy - particularly if there is a thermal plane required on the back
of the board.

Handsoldering of fine pitch quad packs, while possible, tends to be highly
skill dependent.  Results can vary considerably dependent on the individual
who performed the basic work.  Vias in pads add to the complexity and
frustrations of this task.

Literally any (or all) vias on a circuit board can perform as "thermal vias",
including operational electrical vias under part bodies.  There are a number
of via fill compounds available from DuPont, Lackwerke/Peters, Enthone-OMI and
others, with varying heat transfer coefficients.  These materials are applied
prior to solder coat and solder mask application.

Movement of heat from the part to pads thru the leads does occur, though its
rate is dependent on the design of the individual part.  Thermally conductive
adhesives, applied prior to part placement, can move heat efficiently from the
part body into the circuit board.

Quite a few of us out here are using some or all of the above in production
with varying degrees of automated placement and soldering for electronic
products destined for severe environments and military applications.
Obviously, the specific details tend to be proprietary to the user.

If this task is to be conducted only on a few units, then it can probably be
accomplished as described.  If any production volume is contemplate, it would
certainly be wise and prudent to consider the alternatives.

Regards - Kelly

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