Designer here. There are several points to tackle and it's difficult without context, but let's go one by one.
> I'm guessing you like me, get very critical feedback on them since anyone can easily be a critic.
Handling critical feedback is one of those soft skills that are honed by time. You must learn how to separate useful from pointless feedback, and you must not associate it to your own person, as in feeling worth less over negative comments.
Most design feedback is irrelevant, if you implemented it your product wouldn't be any better or worse. A little bit is beneficial or harmful, and it is important that you are able to identify which is which.
You might think that people with more experience are able to give better feedback, it's partially true, but it all boils down to having solved similar problems before. Trust advice that starts with "I once did something like that and..." or such.
> One issue i've found is that only YOU really know your application and designers often want to "change everything".
In the end, what matters is that your users get it, not you or the designer. Programmers often design systems that closely represent the structure of their application, or take shortcuts because something that makes sense to the user is difficult to implement so they scrap it.
> Anyone have PROCESS tips, tricks, suggestions or other thoughts about effective UI improvement?
Hallway usability testing is your best bet. But don't ask people what they think, assign tasks and watch them complete them. Clarify that what is being tested is the interface, not the users. It's hard, but suppress urges to direct them.