@Nik
I think I've gone over this with you, but I'm not saying the systems in PW games weren't fun, I'm saying they degraded the game. In Perplexicon, it wasn't an issue, because it was a PvP game where everything was equal-opportunity brokeness. Only the PvE suffered, and it was never really the focus.
But in ER? Tinker was terrible. Power creep did not improve the game for anyone, though it was fun to fuel. Tinker was good as a flavor thing, and as a puzzle to solve, but the fact that it actually granted rewards was a significant flaw.
A crafting game is gonna have the same problem. Either everything will be designed and roughly balanced beforehand (==never being finished), or people will break the system during gameplay. It'll run into the same problem ER had, where actually being challenged by foes without them being arbitrarily powerful is nigh impossible. Of course, if the meat of the game is just crafting, with any actual PvE challenge being a negligible part of thr game--Like Perplexicon--then it could work well. I just don't think that's how it would work.
As I said, we are likely to have strongly disagreeing views here. Frankly, I believe that Tinker was the best thing that had happened to ER, and while you may be right about it being good for flavour, I think if there was no real potential prize at the end, it wouldn't have been half as fun because of the off-putting nature of useless activity; though it might be just me. Still, I'll grant that the carefully designed system of "okay, but only the very best items get the green light" went down the drain right when we captured Hephaestus, so I guess that was the turning point of it; there's certainly a very big difference between "your design has to be sensible and okay to be allowed" vs. "your design has to be clearly top-notch, far better than anything already in the Armory, and no more expensive at that".
I haven't played Perplexicon, and I know about it only by second-hand accounts, so I can't say anything about it. But I can certainly say this about ER balance and Tinker: Tinker
did not impact the power creep in any significant way, and it was
not the power creep that killed ER fun. It was the wild (and, yes, only growing) imbalance between offensive and defensive measures. Had the enemies defensive power been scaling at roughly the same pace as the growing offensive power of the characters (and vice versa!), PvE wouldn't have suffered that much - or at all. Yes, this might have required some authorial guidance and GM fiat on the meta-level of equipment and stuff - or really, really planned for that beforehand - but that would have been the cure for the illness you accuse Tinker of facilitating. (The Space Wasp mate of the Eater of Cold might have been a very good example of it - it wasn't exactly killing everyone present on the spot, but it was literally practically unkillable - and thus forcing the players to look for other way of dealing with it apart from the usual "Repeat fire until it's dead" doctrine of HMRC, and that was very good.) In short: it is very possible to balance things on a sliding scale against increasing power of characters without said things being overly, incredibly lethal, and Tinker does not preclude that in any way - in fact, (perhaps if slightly incentivized, or hinted at) it could actually help if it was used to amplify the staying power of characters, thus offsetting the unfortunate (yet justified and necessary) deadliness of things that oppose them.
Now, power creep itself is something that some people abhore (and some people - like me - celebrate), but that is a design choice to be made by GM, so I'll leave it at that.