IMO it isn't about whether or not to build them. If you are really looking at balance issues then you want to go past something deserving to be in the game. You want to look at whether the building is attractive enough to cause someone to hesitate on the decision to build this building or another one because they are both actually good to build. That sounds like balance to me. Giving buildings multiple uses moves them out of the niche or specific need category into a part of the strategy category. If the Medical Lab could use a bump then I think it stands to reason that the Hospital could use one too. It is also good to remember that the late game really needs to be picked up and every advantage put in to help with the happiness system is going to help the AI. I really think we need to make it easy for the AI to avoid happiness issues.
To your point here, I think that the med lab and the hospital are both good buildings from a bonus standpoint.
I look at these guys and say "I want to build you". I often don't because it takes so long to build them.
With our current change, I can build these buildings much faster than before. That is a very powerful change, and I just don't see the need to pile on even more. Lets try it out with just the cost reduction and see if its useful enough.