Regarding the Alvida VS Tsuru debate...
I think it's worth noting that Alvida's Romance is currently the only way to farm her special manuals, while Impact Usopp manuals also drop during Brook's fortnight. It's a ways off, but better than waiting for Tsuru appearance No. 2.
Zephyr is coming up before Brook, but the only team I've seen that requires a lowered Impact Usopp cooldown is Marco x2, which also requires prior Garp farming to have Usopp/Garp specials land after 16 turns.
On the other hand, the drop rate for Alvida manuals sucks, the Pirate XP sucks, plus she's not sticking around very long. Odds are only those that gem and wait for the next Special rate-up event will put a dent in her cooldown, and using gems only really seems worth it if you're at or near 90 stamina, to get three runs out of each refill. Using gems also seems wasteful right now, with Rayleigh Sugo and Mihawk #2 theoretically around the corner.
In my opinion, it really doesn't matter either way. As far as I've seen, there are no strategies that I've seen that require Impact Usopp or Alvida at MAX cooldown. Of the two, Alvida at MAX might be required to hold out against future raid bosses, but it also feels like she's overdue for a medium-rarity manual drop in a new fortnight, one that would probably show up before said raid boss.
Outside of manuals, Alvida Expert does provide a pretty good chance for Red Daimyo turtles and Red Pirate Penguins, for those who haven't evolved Monster Chopper yet.