Micaiah worth pulling?

Yes. She's definitely worth it. Her kit is incredibly antimeta - requires very little skill inheritance to dominate the arena. Plus good arena scoring for a mage due to her unique B slot.

You should be able to make do with your current bunch of Blue tome users. Micaiah is really handy for dealing with Reinhardt and other Magic users, as well as Armored Emblem, but if you aren't worried about those, just continue saving.

She has great skills and I would pull for purposes of skill fodder. But I don't think she's worth pulling to use. Then again I never really cared for infantry mages.

The biggest problem is that she holds a very niche role in countering a set of units that she can't always handle on her own and is rather weak to herself due to having low Spd and Def. In most cases, a failure to KO in one attack means she will get doubled in return and they will KO her.

I think the only interesting thing in her kit is that Sacrifice might make her the closest thing to a viable Brash Assault user in the game.

Although she has effectiveness against Armors and Cavs, I didn't have any trouble fighting her with those teams, so it's really a toss up. If you have good teammates with her, she can be quite good, but if you're up against a well-built opposing team, she will crumble. Hell, I think I killed her with Zelgius once cause he outsped her and doubled on his counter.

If you’ve spent 20 orbs and didn’t get anything 5*, I’d recommend dropping another 20 and seeing what you can get. Any of the 3 focus characters on the RD banner are good pulls, and as a fellow F2P player who dropped 40 orbs on this banner to this point, it’s had a crazy knack of giving people ridiculous luck; some people have pulled 2-3 Micaiah on a single slate, or Micaiah and Sothe together. Me, I pulled a Sothe and a Lute, which I arguably think was better than pulling Micaiah.

Well, I personally think she's definitely worth having simply because she's just so damn versatile. She can check both cavalry and armoured units simply due to her weapon, duel mages with her insane Resistance, and finally check red units with her Affinity, not to mention how she's also one of the best users of the new OP QR Seal. After testing her with some different builds in Arena, she immediately replaced the blue slot on my team, competing with +2 merged Reinhardt and some of my best IV'd and most well-built units. The enemies I usually run into in Arena are between +5 to +10 merged and Micaiah can still handle them perfectly fine without any merges of her own. If I had to compare her to anything, it would be Brave Ike except with a usable player phase build. Let's also not forget about Yune.

Now, despite all that Micaiah does suffer some weaknesses, namely her Speed and Defence which brings down both her nuking and tanking potential, causing her to die to green mages and most physical threats, or potentially miss ORKOs on certain reds which alongside her slightly niche playstyle as a ranged/meta counter makes her somewhat underwhelming compared to other blue units.

So, do I think it's worth summoning for her? Definitely, she is by far one of the most balanced units that's been released in Heroes so far and has so many different strengths you can capitalise on and build around. However she's not mandatory to have and might not suit certain people's playstyles, but with all that said, do maybe one full summon/snipe and just wait till the last day so that we have more information on the future banners before making your choice, there's absolutely no rush.

It's a no if you're F2P.
I'm pretty confident to say she'll definitely in the next legendary banner, so if you like her, it's better to save your orb and wait until then. You already have pretty solid blue mage, getting her isn't an urgent matter.