Come on DP! Don't sulk. You've been super quiet since finding out many folk here are old enough to be your grandpa father .
Geeze man, can't I step away from this place for a couple of hours without a search party being formed?
I'm trying to take some of Bryce's suggestions (about interestingly detailed magic items) to heart.
Your attempt is better, but still really mechanically clunky. Slows down play. If I were a player who found it, I'd have to remember three paragraphs of rules just to use this thing.
When Bryce speaks of making a magic item interesting, it doesn't mean that your items have to do a ton of different things (which necessitate a ton of different caveats for its user to remember). It means makeing the item memorable, and worth holding onto for reasons beyond the mechanical effects and bonuses.
Your attempt here...
>throwing dagger, burrowing: 1d3 additional damage/round with successful hit, until forcibly removed. Second throw is +3 to-hit if used as a pair against a single target.
...is a good route to condensing things by starting small, IMO. As a DM, reading this I would know exactly what that thing does at a glance - it burrows into flesh (causing further damage), and comes as a pair that offers a bonus if used together. As a player, I can better remember mechnical considerations that fit into a single paragraph.
Throwing what Bryce says onto it, you add character to the thing, a touch of intrigue. The advice of Bryce is nice, but only when used as spice (Rhyme time!) - doesn't require much, but makes a big difference.
Observe your dagger now:
> A Heartseeker Dagger bears a jagged blade set into a stylized silver hilt depicting a mournful figurine - an outreached arm serves as the dagger's guard. When held, the faintest sound of crying is heard by everyone but its handler.
Heartseeker dagger: burrows into flesh for 1d3 additional damage/round with successful hit, until forcibly removed. If used as a pair against a single target, second throw is +3 to-hit.
This is, I believe, what is meant by adding just that little extra to your items.