There are a lot of open spaces where the air inside the chamber escapes, the front door, open holes in the back panel and open spaces on the bottom of the chamber
I guarantee you if you take the time to close off those air gaps with something like foam tape that your chamber temps will reach temp quicker, maintain temp better and reach above the recommended chamber temp
Use caution though, too high of a chamber temp can have a negative affect on components inside the chamber like the board on the extruder, possible heat creep, and belt wear to name a few
I personally agree that an active heater for the chamber temp would be a great idea but the caveat would be my previous line about excessive heat on the internal components if the chamber temp gets too high
The most beneficial aspect of an actively heated chamber would be time saving because the bed is capable of heating the chamber, just very slowly 