At the moment it's complete poop lategame. Say he has 1000 HP. 1000 x .3% is a measly 3 health a second.
Now say its lategame. You're rockin' 4500 HP. Youre passive is now at 13.5. Add Spirit Visage and its an extra 2.7. Now we have a grand total of 16.2 health per second.
Lets look at Garen. At lategame, he has 2.0% of his max health every second. If he has 4500 HP, that gives 90 Health a second. With SV thats 108 health per second.