The first positive thing that I have to say about the Warpsmith is that his model is very nice. Ok, that's aesthetic opinionated crap over and done with, let's get down to analysing this thing in a way that is less objective.
The Warpsmith is 5pts more than a Dark Apostle, and comes with his own special shenanigans. First off, as a parallel to the Techmarine in the Space Marines Codex, instead of improving one of your pieces of terrain, you get to worsen one of your opponents. Although you can't use this on area terrain. I would say that this is better than being able to improve terrain. Yes you can take an Aegis Defence Line and give your units a 3+ save base or something like that but at the end of the day, it comes down to how dependant upon terrain Chaos Space Marines are.
If you're more dependant on it than your opponent, then you'll want to improve your own terrain, as your opponent won't care too much if you degrade theirs. But if you're playing against an army that is dependant upon it (Dark Eldar, Tyranids), they're going to hate their cover saves being reduced more than you'd enjoy your cover save being better, if you get where I'm coming from.
His second piece of shenaniganary is to do with his ability to repair vehicles. Incorporated in the rule which allows him to do this, is a second paragraph which allows him to mess with enemy vehicles too. Essentially, if he hits it, its weapons get hot (Leman Russ Punisher fun), when I saw this I also thought, hmm, Stormtalon, that'll come close to me and can get a decent number of shots off. But King Kelly has thought of that, the Warpsmith rolls to hit with BS rather than a fixed number. Balls.
Other than all of this, he also comes loaded with a crap load of basic wargear. He has a 2+ save (not so basic) but no invuln, but he also comes with a piece of wargear that gives him extra attacks, a flamer, a meltagun and allows him to fire 2 weapons. He can also take Veterans of the Long War and standard Chaos Artefacts, Rewards and so on.
But do you want to load him down with that extra stuff? The reason that you'd take one of these guys is for the shenaniganary surely. Yes, he's not bad in a fight with those 4 attacks base but when considering his base cost if I wanted a brawler I could do a whole lot better with a Chaos Lord, who is also fearless. So, don't bother with that. Maybe go with Veterans of the Long War though, that's always nice to have.
So, is he worth his 110pts? I think he's not bad for it. He's very versatile, being able to deal with hordes and vehicles with his weapons, he's good in a fight, although I think that an invulnerable save would be nice - if you really want to spend points on him go for Aura of Dark Glory then – as he strikes with an Unwieldy weapon. And he also comes with some nice special anti vehicle rules as well and the breaking down of opposing terrain is a nice force multiplier.
So, if you're looking for a versatile HQ unit without having to flick about the book for that perfect upgrade, why not go with the Warpsmith. Plus he's one cool looking model.