Although I'm a huge mecha fan I havent watched a lot of classic series like those you listed, mmiguelce. But I know all of them (aside form Mekanda Robot) mostly thanks to the fact that they are in many of the Super Robot Wars games. And to answer your question, sticking to the mecha genre, there has been a lot of improvements over the years. First mecha anime was shallow and mainly focused on action and never the cahracters. This changed over time and today with series like Gurren Lagann, Godannar and GaoGaiGar show you can add more things like mixing concepts, focusing on character development and just outdo all you competitors in awesome action respectively. Super robot anime is still here and have grown strong in the last years.
Another side of all this is the Real Robot subgenre within mecha, started with the 1979 classic, Mobile suit Gundam. That anime and Evangelion has saved mecha anime from becoming extinct in my opinion and without those shows we wouldn't have seen great hits like Macross, Code Geass and Full Metal Panic, to mention a few. The older anime in this genre, and some other cant really compete unless they are extraordinary in some way. Many are well worth a watch though as I love to see epic movies like Macross: Do You Remember Love and you can still watch series like the earlier Gundam shows for their cahracters and politics, or a Go Nagai story for the violence and action. Its just that many newer series have grown into more dimensions and tries more things instead of repeating the same old combination sequence to beat another bland monster of the week for 50 episodes concept that was standard back then.