Looking to upgrade Adcom GFA555: Parasound?

This is my third system.  Honestly, usually used for semi-active or background music.

Speakers are vintage Wilson Watt/Puppy 7.  Source is an Eversolo dac/streamer Into a vintage Classe DR5 preamp.  Amp currently is the aforementioned Adcom: bought it new while in college 40 years ago!  The sound is pretty good, though a bit “small” and closed in.  

Considering replacing the amp with a Parasound A21+.  Thoughts?  Am I wasting my time?
 

Target cost to upgrade this rig: less than $5K.

Thanks!