Contests with the best results come from active clients. Energy creates energy. The best thing you can do is login a few times per day, update the rankings, and leave at least 1-2 comments per Designer. That will do more for your contest than any prize increase would.
Public comments on your current feelings are also very helpful to Designers as it allows them to understand what your current situation is. Designers often pass over contests that have little activity in the private or public comment area for the contest.
We do ask that you refrain from referencing specific Designer's entries in the public contest thread. However, you can mention things like your current feelings or offering new ideas that have not been mentioned by you or submitted by Designers.