ISTR somebody mentioning a paper, about three or so years back, that
took these effects into account, and concluded that such an enterprise
would still be profitable under reasonable assumption (even about the
cost of getting to the asteroid etc.) Henry?

Here are some cites which were posted to usenet a few years ago.
These are also at http://www.panix.com/~kingdon/space/mining.html
along with a few online links.

* M. McKay, D. McKay, M. Duke, eds., Space Resources:Materials,
NASA SP-509, v. 3, US GPO, 1992 (P. 111-120 cover asteroid
mining).
* J. Lewis, T. Jones, W. Farrand, "Carbonyl Extraction of Lunar
and Asteroidal Metals", Engineering, Construction, and
Operations in Space (eds. Johnson & Wetzel),
p. 111-118. American Society of Civil Engineers, New York, 1988
* J. Lewis, M. Mathhews, M. Guerrieri, eds., Resources of
Near-Earth Space, U. of Arizona Press, Tuscon, 1993. (Too many
good articles in this one to list).
* J. Kargel, "Metalliferous Asteroids as potential sources of
precious metals", Journal of Geophysical Research, v. 99, no
E10, p. 21129-21141, October 25, 1994. (The first attempt I've
seen at developing price elasticity curves for raw materials)
* C. Meinel has a nice article from the 1985 IEEE EASCON on mass
payback for various asteroidal return scenarios.
* Lewis and Lewis, Space Resources: Breaking the Bonds of
Earth. (Don't have a complete citation for this).