Based on reasonably extensive practical experience, I've found that you can get an amazingly useful feel for radiated energy by using a transistor radio placed in close proximity to the target and tuned over AM and FM bands. This is useful enough to get an excellent feel as to whether your system is likely to be terrible, reasonable or (probably) extremely good.
Obviously this is utterly informal and subjective, but you get a feel for degree of severity and more. You'll quickly find the relative usefulness of AM and FM bands. Sometimes breakthrough and intermodulation on the lower band may be more useful than direct reception in the FM band. Even if your device has no formal radiation outputs in the bands above, there's a fair chance that, placed close enough, you'll still get useful results.
Also useful is tuning a TV across its whole tuning range and observing the screen. Best for this are wholly manually tunable - the ulra cheap portable black and white ones with something like a 6" screen used to be very handy for this.
Of these two methods tha radio is probably the most useful. Best are radios whose whole tuning range can be swept with single twist of the wrist. That is, you don't want some thing geared down that takes many turns to scan the range - although that probably has its place for spuries that are in a known location.
When you can operate a transistor radio on or within a few inches of a device under test with essentially no interference it tells you that you are winning - or that it's not turned on :-).
