The time trial is designed for "walk up and play this game NOW" scoring contests. It doesn't work for an un-monitored contest where people can keep trying again and again for a week, because then everyone ends up with the same score in the end.
You could say the same thing about single player mode if every one will keep trying like they did in time trial. Time trial mode is designed for contests, so there are lots of ways to find the best methods of getting high score. I'm not sure how well Spriggan's time trial mode is designed, but if it's anything like Soldier Blade's, there is going to be some good competition. In Soldier Blade's time mode, there are tons of little secrets of getting a higher score, check out
here for a guide that shows all the tricks. We like to hold these video game tournaments in my house and one time I chose Soldier Blade's 2 minute mode for it and there were some interesting results. I had more experience with the game than everyone else, knew some of the hints and tricks to get a good score, blasted away a bunch of stuff and didn't get hit once, yet a few unexperienced people beat my score and died a bunch of times, one of the people being someone who had no experience with the game at all! So if Spriggan's time mode is similar to Soldier Blade's, I think we will get very mixed results and have a fun time seeing who can manage the highest score. Not only that, but more people might be interested in competiting in this if it was a time trial mode.