Depends on how often you raid. If you raid a crap ton, then you'll won't need it, because you'll be getting tons of Dialga. (At least 4) Also depends on your availability during the community day. Metagross with Meteor Mash destroys all current competition. (Except Dialga or whatever comes after in following gens) If you plan to splurge all your candy into evolving Beldums, you won't even need Scizor. It's Bug typing doesn't offer much, but I suppose it helps against the occasional dual typed Ground/Rock raid bosses. (Rhydon/Golem) but I think they'd still come out the same in that situation because Scizor doesn't have too much meat on its bones. If you say yes to both of my questions, you should know the answer.
Scizor Power up?
I currently have a 1700CP Scizor with 89 iv ( 14 11 15 ) and bullet punch and iron head. Power up? It looks badass and I only have 35 scyther candies. Save for another Scizor or power this one up? Is the iv good enough?
Answers
I am usually the kind of person who thinks one attack IV doesn't matter. For a steel set it is acceptable. However for Fury Cutter, and other very weak and fast moves the extra IV makes a difference more often.
I generally don't power up mons anymore below 95% with some exceptions. As you are aware scythe is one of the more rare species in the game. You don't see them in the wild very often and while they are in raids sometimes even if you do catch it you're only getting 3 (6) candy per catch as opposed to 10(20) for many of the raid bosses.
Power it up if you really want to and if you have plans to use it. But consider how long it will take you to get another one powered up should you get a real winner.
Scizor is rare enough here that I wouldn't expect to find one over 90%, and evolving a second one would be kinda expensive.
He looks badass and he performs well but he will find waaay better use as a bug attacker, cause tomorrow you will get metagross and Scizor won't be able to compete. So if you like Scizor, just power him up and TM him to Bug moves in my opinion
Scizor was a decent steel attacker when it came out in Gen2 (decent being relative, there haven't been any really good steel attackers until tomorrow, when Metagross gets Meteor Mash).
But Scizor is one of the best bug attackers in the game, and it's secondary steel typing provides many useful resistances (and a double weakness to fire). Best use is to TM to double bug, as was said above. Still not sure if it is better than Yanmega or not, though.