I know that fans complained that the widescreen DVDs made the effects look worse than they did on TV, supposedly even accounting for changing standards and sharper TVs. I've only ever seen the DVDs but the early season special effects look really awful, so that's where I'd count on the greatest improvement to be.
I own the dvds but lent them out a few years ago and haven't gotten them back. HBO Max is streaming the show in the US, and they have the Studio Ghibli catalogue too, so they're a worthwhile streaming service. So I'll probably give those versions a go some time in the next year.