Is it worth evolving bad IV shinies?

Depends on what you're out for really. I have a low-ish (40> ) iv shiny Charmander and mareep I got, but they are high level and I likely wont be powering them up after I evolve them to get their moves because I have very good iv versions im focusing on. In the case of my shiny larvitar, its got ~64% and 14 atk, so even though its over all iv's ant the greatest its level 35, its still going to be a raidwrecker like my 98% lucky nonshiny. If you're goal is to get a high CP shiny of the pokemon and the shiny you have is high level and If you know you wont be putting much candy into it, go for it. I'd say go for it if you want the shiny and its a pokemon you'd like to use/have, as I believe personal like of a pokemon >>> than any iv's.
But really IV's arent as big of a thing as people make them out to be, while higher iv's are better, in truth theres not some huge gap in preformance unless it misses some break or bulk points which even then, doesnt really have a huge gap as well.

Really its up to you what becomes of them

Well, for PvP, with the CP caps for two of the leagues, IVs won't matter much, if at all. If one of them powers up to just under 1500 CP, or just under 2500 CP, it might be a good option for that league, and you'd have a shiny to fight with. If it's a starter, or Larvitar, evolve it before the end of the event to get the special move.

Otherwise, wait, and decide when we have more information about how PvP works, and have optimized the pokemon choices for it.

Remember you can always reroll the IV's with a friend, especially when doing a lucky trade. I have a plan to exchange our shiny Eevees with crappy IV for 2016 Pokemont with my friend, getting a guaranteed lucky.

Evolving one shiny to complete the dex entry is nice, after that ypu should evolve one woth good IVs (be it shiny or not). Once you have those two sorted out both are good as trade material, but of course a shiny with and exclusive move will be more valuable. If you plan on keeping and using the mons you should evolve good IVs ones, else shinies can net you some really nice mons if you are willing to trade so they are indeed valuable!!