Yes, Everything.
We are no longer in the position of cherry picking buildings, we got thousands of one up kits and renovation kits staying all this time in titan, game inflation is still going.
Maybe some old 2x2 buildings that are not giving goods to not be worth being upgraded to the last era, but the others should do, having goods and attack stats, population increase and more.
Anyway, when you will want to upgrade them, a window will appear and everything that interests you will be there, comparison of old to new era, so you wil conclude if it's worth or not, according to your playstile.