I looked but couldn't find a similar post

Is there any way to make the spell more powerful?
I know each stage of vampirism improves it slightly, but not much.

Is there any other way to make it stronger?

Only by advancing through the different Stages of Vampirism. Even then, it doesn't get very strong at all. It's pretty much useless (IMHO) by level ten.

You could try this:
http://www.youtube.com/watch?v=UTMJKqUgxZY

Not sure if it still works though or if it has been fixed in some patch.
It also remains questionable if there's any point, casting a restoration spell and having either a weapon or shield equipped would probably still remain a much better option. Unless you do it for some roleplaying purpose ofc.

Thanks

http://skyrim.nexusmods.com/downloads/file.php?id=7873