You might want to take a look at the aggregation possibilities I've been
finding at http://www.mcvax.org/~jhma/routing/ (everything there is updated on
a daily basis). Based purely on origin AS, for any AS where any form of
aggregation could occur, it lists which new aggregates should be announced (in
place of individual specific routes), and which should be withdrawn (your
"useless punchout" case above) or advertised with a different origin (because
all the address space covered is being announced with longer prefixes from
another AS).
Since today, there are also some pretty(?) pictures showing prefix length
distribution from my view of the BGP table.
Regards,
James