Oh, we did downrank, but we downranked flash heal. At first, before you get some good gear going, yes, you'll have to conserve what little mana you have, but once you are BWL-geared, you just spam flash heal and renew in an attempt to meterwhore and please the loot council. As a Shaman, you spam chain heal, whether downranked or not. You (generally) don't meterwhore only on the last bosses because they are longer and you have to be a bit smart about it, but that's it. You certainly can attempt to pick and choose what heals to use at any point, but you'll very quickly realize you aren't doing anything except stop casting because everyone else is using their fastest heals to try to meterwhore. This is my experience in Kronos, I didn't play a healer during the actual vanilla, but I doubt it will be completely different in Classic, just because this is a symptom of the 1.12 talents/itemization. Also, keep in mind that I was in the best guild on Kronos, we got a bunch of server firsts after BWL, so this might not be the same for every guild.
And before anyone says "but private servers got everything wrong" a) no, they didn't get everything wrong in the context of how Classic is going to play out, aka 1.12 talents/itemization, it was close enough, and b) ok, we'll see if Classic is tremendously different.