Invision does offer resending failed queues. It probably is somewhat different from Syris (I haven't used it, so I don't know), but you can definitely set it to resend failed sends with a choice of how many times to retry before giving up. Obviously, it has to give up at some point or you'll eventually have thousands of queues trying to resend just from people who aren't set up to receive files. I will check out Syris and see what exactly it does and maybe it can be considered for Invision. We'll see.
As for the theme that comes with Invision, I'm not sure how it looks like XP. If anything, it looks more Win95-ish than mIRC by itself with the new buttons. Still, as you found out, you can easily change and customize the look with the Theme Manager.
And with regards to Invision's ease-of-use... yes, it really is a more advanced script and not really designed for the first-time user. It probably never will be. That said, we offer help both on IRC and in the forum for any questions people have. We are also (slowly) working on a help file that explains everything. It's slow because it's time consuming and I don't enjoy doing it, so I only work on it occasionally.
Anyhow, I'll see about checking out the Syris resend feature, but if you can tell me what is different from how Invision handles it, I'd appreciate it.