I'll go back a few years for you.
Real Ghostbusters: When the series added a syndicated weekday strip, Lorenzo Music was replaced with Dave Coulier (Full House) as Peter, and Buster Jones took over for Arsenio Hall as Winston. Mind you, Arsenio rebounded from that rather nicely with a successful talk show that ran for 4-5 years.
Super Friends: Bill Calloway took over for Norm Alden as Aquaman beginning with the Challenge season (1978) and was closer to Marvin Miller's work a decade prior than Alden was, anyway. 6 years later, they recast Wonder Woman and Jayna, though Shannon Farnon (WW) & Alden would return to do a bit with the Powerpuff Girls several years later. Also, as we all know, Adam West reprised as Batman, with Olan Soule moving over to voice Prof. Martin Stein.
Real Advs. of Jonny Quest: About halfway through the series' run, they made wholesale cast changes. Never could warm up to George Segal as Benton Quest, or Robert Patrick as Race Bannon. IIRC, John DeLancie & Robert Foxworth, respectively, were brought in.
The common thread? With the exception of SF '84, the changes in the voice casts were upgrades.