Biwiring make any sense?

It all depends upon your speaker's design. Usually, those with biwire capabilities have designed their speakers accordingly. My speakers (Vandersteen) have biwire inputs due to Mr. V. hearing the difference between single and biwire. Others may scoff, but Vandersteen has been building speakers since the '70's, so I take his opinion seriously. Paul McGowan started with electronics and only got into speakers relatively recently.

I would also try to expand your list of speakers. Can you get some audition time with dealers? Nothing beats listening to as many speakers as you can...

Bob

You’re best off to give it a good try for a while and see what you think. It’ll cost a 2nd set of speaker wire.

Every situation is unique, so like so many things in audio, what you can hear will depend on a bunch of things, so try it and decide for yourself vs hearing about it second hand.

Good advice, while auditioning speakers at a dealer can be fun but nothing like doing it in your home. Dealer quality is not quite the same as in the past. I used to have a part ownership in an audio store back in the 80's.  This is another way of saying it could make you crazy.  I've got a pair of KEF LS50's and like what they do, just a bigger room would benefit from something else.  I like the concept of the mid and upper range drivers originating from as close to one point as possible, but freeing them up from the low frequencies would be a good idea.  I've done that before on a much bigger scale. 

What about biwiring with silver for High frequencies and copper for low frequencies ?

I do this with AudioQuest KE-4 (15 AWG pure solid silver) up top and Mont Blanc (12 AWG solid copper) on bottom. Used to use this in my main rig, and now brought it back in my 2nd rig. Always liked this combo (going back 15 years), and still like it now. Have compared it to many other AQ models - symmetric double bi-wire, internal biwire, single wire. There’s 2 cable configurations I’ve liked better (both much more expensive), but I like this combo better than all the rest. The AQ hybrids - with copper & silver in one cable - are quite good, but no more effective that this mixed biwire, IMO.

The knock against this approach would be a sacrifice of "coherence" from the asymmetric biwire - but I don’t hear ANY issues with coherence here. Silver helps bring out detail and sparkle. Copper keeps a nice overall warmth. And it all blends nicely. Speaking of coherence worries, my Tannoys pair a metal dome with a large paper cone - and they’re still incredibly coherent, to my ears!

My experience is it depends. 
 

I have listened to different cables and ultimately chose Kimber Kable bifocals XL. I am positive with enough time I could have found another excellent solution. 
 

Enjoy your journey!