here's what you do about spamlining:
1. play for reputation, not valuation
2. don't play in USA or China (or europe in worlds that start 1990+)
3. Play in smaller worlds
it's obvious that "spamlining" is the best way to attain the valuation trophy, so if you want to get it, learn to play that way. As has been said here already, it's within the rules of the game.
Playing for reputation is not really challenging. Quite easy to get a 100% reputation.
The best way I found to avoid spamlining is the S1 world (one hub/terminal limit). More difficult for spamliners to kill competition, although some do succeed.