NSP ... New Information

Suppose that IP space were not a problem. When IPv6 comes up all around,
it certainly won't be then. You can have and waste all the IP space you
could imagine, since we'll be numbering every atom in the known universe.

And suppose we have ASNs a plenty.

Would Sprint, Digex, and AGIS still be trying to cut out so many routes?

It has nothing to do with available IP address space. It is purely the
number of routes in the "global" BGP routing table. Doing rout filtering
a la Sprint is one way to enforce better aggregation and cut down on route
table size.

Also, in general, the longer the prefix, the more a route tends to flap.
Route filtering is one way to help cust down on the number of BGP updates.

Are any other ISPs doing this filtering?