How can you tell if a speaker has impedence dips?

It probably won't effect anything really. The Paradigm's are of such a load that an amp will find them easy to drive. The only way to know impedance for sure is a test whether a review or manufacturer. If the amp runs hot, simply parallel the speakers. This will keep the impedance up. A bridged amp will like this load better anyway. When you bridge, your amp will see an 8 ohm load as a 4 ohm, a 4 ohm as a 2 ohm and so forth.
I do agree with the above poster about deterioration in sound quality when bridged.

My old 1980s vintage PS Model 2 amps sound WAY better bridged. It's not even close. I'm driving old Rega 2-way speakers with them.

Folks,
It's always a trade off. One amplifier would feel better when it has a normal load and another one would feel better working as a welding machine with literally short circuit(upto 1 Ohm dips) depending on power supply in general so the benefit might be better output characteristics for certain load impedance.
As to voice coils, the smaller the voice coil, smaller ressistance and more current demand to drive it.

Meech33,

Here is the link to the Stereophile review done in 1998:

http://www.stereophile.com/showarchives.cgi?628:3

I'm "sending" you directly to the measurement page showing the impedance & phase plot.

Lowest impedance is 4 Ohms @ approx. 200Hz (mid bass region). Music has a lot of presence in this region & it is a bit unfortuante that the impedance dips this low in that region! Your amps better have the power to compensate! This conclusion is, of course, based SOLELY by looking at measurement results. Many times results mean squat & the speaker is just fine w/ moderate power!

FWIW