I am willing to sponsor packages, but generally not willing to take over the maintenence. I've got too many other things going on, so I would do a bad job if I tried to maintain more packages.
When sponsoring, I prefer being approached by the package maintainer on IRC (pere on irc.debian.org and irc.oftc.net) with the URL to where the package can be downloaded. This is a low-overhead solution to me, and I do not accumulate a large backlog of request for sponsoring (as would happen if I tried to gather sponsor request using email. :).
The packages should be lintian clean and tested in pbuilder or similar, to make sure the dependencies are correct and obvious problems are found. I primarily sponsor packages going into debian/main, so if the package isn't acceptable for main, there is normally no need to approach me.