Is impedence so important for a pick/phono combo?

Yes, it is important. Especially at the higher quality and price levels, where very small sonic details make a difference.

The impedance loading for a cartridge not only affects the sonic flavor of the cartridge, but can also influence the output level and also the internal damping behavior of the cartridge.

It is important to note, however, that not everybody agrees about what is the best sounding load for many cartridges, and it can be somewhat different depending upon your system and tastes.

A phono preamp that allows a wide range of loads to be applied to the cartridge gives you the ability to experiment with loads that might sound best to you. In the absence of multiple load settings, some makers give you the ability to change precision resistors to the value that suits you. You can then buy a range of these resistors, and do the changing yourself.

Allow me to add some comments...first I want to say that I am no tech person but I understand TWL's response (I hope).
I have had an opportunity, this weekend, to listen to the Aesthetix Rhea phono per-amp. This phono amp allows you to set load and gain very easily. I have a Helikon cartridge that is recommended for a load of 100 to 47khtz (??). I had been using my ARC PH3se previous...and it was loaded at 47khtz.

Big difference when I went to the Rhea and set it at 47khtz and then went to 500!!! There it was..body, warmth, foundation.

Alas, the Rhea started to act up.....it just shut down for no reason??? I had a call into Musical Surroundings and my dealer...they are also surprised. So...here I am...lovin the Rhea but with some serious doubts. The ARC has functioned for me for 2-3 yrs now with NO problems.

Jim White.....any comments??

Today I'm living up to my moniker Bombaywalla 'cuz I'm writing from Bombay, India! Am visiting the home I grew up in & where my parents still live!

As TWL mentioned above, it is important to get the impedance match betwn cart & phono pre correct otherwise one can severely degrade the sonics of the cart. Electrically speaking, the phono pre impedance should be 10X that of the cart. so that it doesn't load down the voltage coming of the cart. I think that you have this already but, I agree, that not everyone agrees as to what the correct value is over & above the 10:1 general rule-of-thumb as everyone's ears are trained different.
The capacitance in the phono pre + that of the cable & the the internal DC resistance of the cart. forms a low pass filter. Wrong selection of the phono pre input impedance can cause this filter to attenuate freq. in the audio band & give you vastly degraded sound.
There is a good dissertation on this on the Hagerman Technology website or on the AudioAsylum FAQ page (in the vinyl subsection). It clearly states the advantages of selecting the correct impedance. It is shown graphically as well & it worth your time to read it.
FWIW.