If you do not download the entire contents of the torrent, you will be forever listed on the tracker as a leecher for the torrent and won't get the type of traffic you would as though you were a seeder. Not to mention, with respect to saving the .torrent files, don't fool yourself. Last year we had a major server crash and lost a number of these .torrent files. By saving these .torrent files you ensure that in the event that the server should ever go haywire like that again, you have the ability to re-upload the torrent and get credit for it.
As well, when you're not listed as "seeding" the torrent, unless you have another torrent that is seeding, you won't get the seed bonus points for having it seeding. I suggest that its within your best interest to fully download the entire contents of the torrent, but ultimately, that is your decision to make.