It will be 65%, as the 30% boost applies to the amount drained, not the amount it will drain.
It says increased, which can,most probably, solve our problem.
Also, Leech Seed, if dealing 10 damage, will damage 13 with a Big Root. This is a similar case, with 30% of the HP healed will be added to the total healing.
Look here for the Leech Seed example.
This question also tells a lot(your own answer) : http://pokemondb.net/pokebase/69224/does-the-root-make-draining-moves-more-powerful-just-heal-more
Note : This is what I feel, after having done the Math. However, if anyone differs, then, I won't deny, considering this is a tricky question. Also, I might be wrong for all I know.