Can one always monitor guard when flying IFR if equipped with two radios?
Not "always" but I would say 98% of the time.
Here's what I do:
(note that all 3 of our club airplanes now have dual flip-flop radios, which certainly helps)
Pre-flight: Audio panel set to Com2 Tx + Rx
Com1: Tower <-> Departure
Com2: ATIS <-> Clearance, then Clearance <-> Ground, then Ground <-> Guard
So, I'll pick up the ATIS, clearance, and talk to Ground on Com2, with tower and departure ready to go on Com1, as given by Clearance. When I pull up to the hold short line, I switch the audio panel to transmit on Com1 and monitor both Com1 and Com2, and flip Guard into the active on Com2.
Flight: Audio panel set to Com1 Tx, Com1 & Com2 Rx
Com1: Tower, then Departure, then flipping in each active frequency along the way as they're assigned.
Com2: Guard <-> ATIS/AWOS/FSS
So, in flight I'm constantly monitoring guard unless I'm picking up ATIS/AWOS (which takes about a minute) or need to talk to FSS (which is rare). The only time I turn it off is if I pick up a loud ELT signal that interferes with using Com1.
So... Again, 98% of the time you can monitor guard, whether you're IFR or VFR. Most of what you hear on there is the occasional mis-transmission of an airliner who's got the wrong radio selected, or ATC facilities attempting to contact airliners or other IFR aircraft after they've accidentally let them fly outside the range of a transmitter without a frequency change.
Or, if the president is out and about, repeated warnings to the people who are about to fly into the TFR.