Of course it's worth it. It shows up as a loss on FD because you're losing all the agility for 1m10s and essentially have no benefit from a trinket. The thing with H-Spine is, nobody cares about the 1m10s on the amalgamation. Yes, it gets a little hectic on the 3rd plate when you want to burn that amalg ASAP before the blood tank gets insta-gibbed, but amalgamation DPS shouldn't be too difficult to make up in the end. Pre-nerf (IE, Tuesday), the important part of the fight was tendon damage, IE the 20 seconds you have KS up for, every minute and a half. Doing the tendon in 2 phases is essential to success, and having that burst of agility on a 1m30s CD was super important to it.
Now, I haven't been in H-DS yet this week, so I don't know yet if the tendon requirement is going to be that bad any more, with what amounts to an almost 20% health reduction on the tendons. My guild is full of people who work 60 hours a week (hence why I'm checking this thread at 5 am, I'm getting ready for work), so we raid F/Sa/Sun, so I'll let you know then. But H-Spine still has a coordination challenge which I think is more pronounced in 10 man than 25 man, and which you'll need to work out as well.
(Oh, and crit > mastery > haste should be fine for H-Spine. Like others have said previously in this thread, you want to proc a LnL via ExpT on the dying amalg prior to the tendon popping. If you can get another trap off on wherever the tank is soaking bloods during the tendon burn, you'll be looking at 2 LnLs at least. You shouldn't really have many GCDs left for cobra shot, diminishing the value of haste on tendon DPS.)