When (if?) I upgrade my plane to IFR I'll need room for two NAV/COMs and an audio panel.
That's a common misconception, "needing an audio panel"!
Newer 150's and all 152's already have provision for all the audio switches you'll need, in the eyebrow panel. Newer nav/coms have sidetone, built in audio amps that are powered even with the radio off, and audio isolation (wired into the switches above) for at least 3 and up to 7 inputs. The only thing extra needed is an audio isolation relay used when dual nav/coms are installed (cuts out the ships speaker on transmit) that mounts behind the panel out of sight. Dingbat is set up this way!
See? I just saved you one whole slot!
