I did a similar upgrade back around Christmas. I was originally using a Raspberry Pi 2 with a HiFi Berry hat (the one that outputs digital). Was waiting for the software program I use (PiCorePlayer) to iron things out with the RP3, before switching to that one. So for the holidays, I treated myself to the RP2 to RP3 upgrade, also replaced the plastic case with the new metal one from HiFiBerry, and replaced the PS with an iPower. Also added another iPower to the MiniDSP NanoDSP unit that is downstream from the PI.
Basically the only difference that should of been audible was the new power supplies. And there was a nice, very noticeable improvement in resolution.