Shorten my speaker cables?

Yep, shorter is better. The amp pulls on a shorter "string" to move the speakers.

Given the distance of typical home setup speaker cable, shorter distance is only theoretically beneficial, given the lower resistance. There is no practical difference (i.e. one cannot hear a difference) between a 25 foot cable and the same cable only 5 feet. Same goes for different length of the same cable. Only when extremely large footage - like hundreds - is considered does length and difference in length matter.

In my view keeping the cables "longer" as opposed to "shorter" is preferable because besides the increased flexibility to move or re-position equipment, I do not terminate the end (i.e. attach bare wire to binding post) and every now and again I like to re-do the ends, albeit each iteration decreased the length of the cable.

Hi: There is research that short cables work best for BASS frequencies. Hence, subwoofers with Amps built; in sound pretty good with out a lot of other technology built in there. I guess if I was building from scratch I would take that into account. Real word solutions often involve "Other people" and room geometry and configurations. I have used Mono Block configurations with a 1 foot Purist Audio Design cable; to the Woofers of my Celestion A3s and BiAmped the top (7" mid and metal dome Tweeter). You can tailor the sound better, but it is a lot more equipment and room dependent. Bass definitely improved even with Adcom 555 IIs bridged! Some of it was cable, some of it was more power bridged. You enter a world of variables here? Most of the length of Cable discussions here have seemed to be consistent with my 40 year adventure in this Hobby. I also adhere to a same length of cable strategy for both speakers. If one speaker is one foot away and the other is twenty feet away; both cables should be 20 feet. This stabilizes the load on the amp? I was told this by an engineering student I went to college with. I believed it, seems logical and before Surround Sound amps; always followed that.

I'm not sure how someone could say with a straight face that a cable X 5 or more longer wont have an audible difference between its much shorter counterpart.

There is no getting around the fact that all electrical parameters involved with the wire in question increase as the distance increases. More Capacitance, Resistance, Dielectric and Shielding influences on the sound and lets not forget the increased chances of the wire acting like an antenna.

Then there is the increased cost of having more wire then is really needed but that is a whole other topic but not an insignificant concern depending on the wire in use with todays sky high prices or esoteric wire @ $1k per/ft or more.

When I was able to use very short (2ft) and rather inexpensive (Mogami) speaker wire in my system I could hear low level details on certain songs that several well known and esoteric brands of wire @ 20X the cost and 8-13ft long could no longer seem to uncover playing the same song on the same equipment. 

In going quasi mono block my speaker wires are now 18", that’s right, inches, and this did make a noticeable difference in mid & high frequency clarity, depth of soundstage, etc.

That said, I did go from using a standard two channel setup to vertically biamping the mains which allowed the shorter cables, so how much of the improvemed sound is attributable to the shorter cables is your guess as much as mine lol.

Martin