it's the only spammable HoT
Blanket Riptides is out most mana intensive healing 'rotation' possible at the moment. Not spammable.
I have to carefully budget my mana
Because of the above.
haste to 12.5%
This is irrelevant. Haste to a percentage is terrible advice. The reason you would gear for haste as a Resto Shaman is for HoT ticks. The breakpoints for these are at numerical values (3764 for example), not at percentage marks.
Mastery at 50%
This is a common misnomer. There is no reason to stop gearing for mastery at 50%. It is your best stat for a fight, or Crit is, or a fusion of the two stats. There is absolutely no reason to just stop gearing for mastery at 50%. 50% is completely irrelevant.
Chaining and Riptide are good glyphs on spread fights
No, they aren't. On an exclusively spread raid fight, Chaining is fine. As soon as there is any stacking you've gimped yourself. Glyph of Riptide is just bad. When you look at your actual use of Riptide, you are picking up a glyph to compensate for lack of good pre-planning.
100% uptime for Healing Stream Totem
Not possible. 15sec duration, 30second cooldown.
it costs almost no mana
Healing Stream totem is considerably expensive. Dropping it on cd is not advisable because overhealing=wasted mana.