The increased melee power is very nice. My main's is now sitting at 121 (not counting the bonus from measure) at cap in SD due to the dagger and a bunch of boosts from reaper Slaver blanks and his armour. I'm sure there are people running around with more than that, but it's a high point for my character as a rogue and the increase made a noticeable difference to damage output along with the high base damage of the morninglord weapons too.
The spy dagger is a nice weapon despite its lowish base damage and issues with DR breaking. I slotted mine with neg levelling augments and still carry them, although I tend to use a Salt weapon (now that I've been able to make one) paired with a Tier 2 TF blinding/paralysis, when needed. The TF weapon is interesting because it causes blindness on the first strike. It helps if you're caught on cooldown for shiv and bluff.
Unlocking those last two slots on the sentient gem meant I had to be quite ruthless about feeding it and now my mules are pretty threadbare. I also fed some raid gear into it that I'd been hoarding for no good reason other than it was hard to get. Having the gem on a BTA weapon made it possible to pass it over to an alt for a purge of his inventory too. But it does mean I have nothing left to put into the sentient gem for this alt, so I will have to start building up a supply of high level items again.
Anyway, I think your approach to ignoring the sets is an interesting one and reminds me of a couple of DC casters I know who are just slotting as many augments for their main stat as possible. If I become less happy with how my weapon is set up I might give your idea a try. The filigrees are dropping in value every day so I think before long only the rare ones will be worth anything at all. I'm sure as you find other rare ones for trade or sale you'll be able to fill in your collection of rares before long at all.
Thanks.