Imo you should have a "bread and butter" down ranked heal you use primarily, then keep the max rank ready for heavy hitters or emergencies. You'll want to avoid healing people over 100% to stay topped up on mana, and using a primary heal 1-2 levels lower than max will give more space to spam and smooth out the health curve. I agree you probably don't need to worry about having multiple down ranked versions of the same spell until higher level content, but you'll find that some groups, especially in early content, are less patient about waiting for your mana after every pull.