First, most of the complaints about Healing Spirit are out of combat. That is why I compared it to Prayer of Healing (also an out of combat spell).
As it is now, HS heals 2-6 times, for d6 each time. What is all this massive healing people are thinking to get out of this in combat? You can only affect a target once per round, and now up to 6 targets (i.e. uses). So, in your party of 4, suppose you want to heal the other three, they each get 1d6 hp over two rounds. Big deal. If you have a full complement of 6 targets (and the WIS 20), you can heal them all for a pathetic 1d6 each. If you want to focus on one target, they are still only getting the d6 once per round (which is how we play it given my suggestion above). Sure, you can heal that single target slowly (over 6 rounds), but to 6d6 (average 21), but it takes 6 rounds! A 2nd-level Cure Wounds (2d8+5) heals only 14, but at least it is in 1 round.
Unless you are completely desperate for minor healing in combat, save the slot for after the battle and use Prayer of healing instead, where the +5 mod could heal up to 6 targets 14 points each.
In combat, Healing Spirit was not overly powerful (1d6 per target per round is hardly crazy). If you are worried about the conga-line of healing, limit the per round use to modifier + 1. We are fine limiting it to only one target per round. It is how we have used it from the beginning. Out of combat it is big, even that way, because it can heal 35 points on average in a minute. We find it very useful. If we have more time and need to share the love (so to say), we use Prayer of Healing.