I think these could be also a "playing preferences" matter of the player.
AtM I play only PvE and there are situations where the Lurker can easily die more than one time and it could happen you don't have Summoning Mastery or you have it in cooldown (in some raids (like Sarn in GT, or The Great Dragon and Dead King in DC) and some mobs in Wellebell (like slugs)), or in astral,).
So?
So you have to gain your blood only with Vampirism/Life Tap and Wandering Fever (Dark Pact, should generate blood drops only out of combat, unless you use it with the % of healt loss to generate 5 drops), until your Summoning Mastery cooldown ends or until you have the time to re-summon it (so, more than 10s to waste w/o healing).
But maybe you're able to make your Lurker not to die because you're caring enough or because your Lurker has a good amount of HP and your heals can keep it alive with a sense (I don't know how you are equipped -gear/runes/glyphs/boutique scrolls and items, etc).
I wouldn't avoid completely it because I think one more blood drop is better than have one less, even if there's a low % to gain it.
I've it r2, but with no rubies. I don't know if the rubies worth it or not, simply because it could be always a "play style" matter. I don't think they could make a great difference, in particular if your blood circle is good enough.
About Delayed Healing I've it and I find it very useful, because I think that have one more heal is always more useful than don't have it, in particular if id influences Blood Shot, being the more powerful heal we have.
In bad situation I think it could make a difference if you need a massive use of blood shot (ie your tank take a lot of damage and the other heals are not enough).
BtW I think that the best way to know if a spell or some rubies worth to invest on them..is trying them out and see, because every player has its own play style and what I find comfortavle you can find it totally useless and viceversa
IMO