Worth it to meld materia to my gear at this stage of the game?

As we all know, crafting is kinda useless at this stage of the game where people are getting their gear from CT, myth and Coil. Hence, there isn't a need for me to craft Vanya robes, rose gold accessories, gryphonskin accessories, etc., is there? Also, with patch 2.2 coming soon, I'm afraid that the current ilvl 55 gear could become obsolete with better crafter gear possibly being released. (there's no information about this, so I'm just worrying for the future).

Also, I was wondering what people are doing to their overmelded gear that have 100% spiritbonded. Do they convert, or keep the gear as it is?

They are a stepping stone. I wouldn't suggest putting 5 materia on them, but a tier 3/4 in the basic slots and one overmeld for a tier 3 is fairly cheap, and very effective.

I am personally keeping my ilvl 70 100% spiritbonded gear on retainer. Tier V materia will likely come out with that next wave of higher level crafted gear, and I'm assuming that ivl70 will have a chance to turn into Tier V.

Short answer: No.

With 2.2 we'll be getting i80/90 craftable gear including tier V materia.
Patch 2.2 is due to release within the next month.
If you can wait 30 days, you'll save yourself tonnes of money, and incredible amounts of time.

I feel bad for players with Particians maxing stat cap :(