Someone please explain the logic of upgrades

To specifically respond to the Audible Illusions, it was a "Class A" component to begin with and is a lot better than most give it credit for being. It is pretty "Tricked" out as it is and Art Ferris has used very, very fine parts. Not knowing exactly which AI you have, the M3A's volume controls were discreet resistors so this eliminates the potentiometers. The coupling caps in the output stage can be switched out. The ouput jacks are of very fine quality already. I cannot recall any wire in the signal path.
I feel manufacturers research the product at its price point and get the most out of it. You can ticker with things and they may genuinely change the sound but then you have to ask "Is it for the better or just different?"
Tube rolling with the AI's will change performance more than some other preamps and this is where I would stay with this preamp.
Art ferris has these preamps sounding as good as they are going to get with their circuit designs.
It kinda goes with changing caps in speakers. Yes you can change the sound but are you capable of making the adjustments for the difference in series impedance and other parameters that actually change the crossover points with a change in parts?
Yes, they're certain mods that do improve performance. Steve McCormack makes a living at it. They're upgrades for CD players that work wonders but at a cost. It is all product dependent. Some products just aren't worth the upgrade. Most well designed products to begin with are hard to fault. The AI falls into this category.

I just remembered, they're are some short pieces of Wonder Wire connecting a few things. Sorry. But what wire would you change it to that would make a difference and stay accurate?

Speaking of an upgraded 8k amp sounding very close to their 17k version: I give you the CJ5 vs the CJ8.Had the 5's for about 5 years and owned the 8's for 3 years.Meaning I owned both at the same time for 3 years.(Just sold the 5's)--System for most of that time was Audiomecca dac. CAT3 for pre. Synergetic active X box.and Montana EPS with Celtic Silver to the speakers. Lots of big buck cords--2 king Cobras---2 AudioMagic Stealth conditioners.---I had some big buck cryoed tubes.
I swear I could take the best tubes;stick them the 5's-- yup,right up there with the 8s.
On to why the amps don't come with the best,whatever feet or cords---- Amp mfg's put their resources on the inside.--I guess Carma might be the exception.

I was drafting up a lengthy response rejecting your learned opinions and opining that manufacturers should use only the highest quality parts, thus eliminating the need for any future upgrades. But, I suddenly realized that, had AI done that, I probably couldn't have afforded their preamp on my meager budget. So I'll drop the issue.

Bigtee - what's tube rolling?

Tube rolling is simply trying different brands of tubes to change the sound from the tubes that came with the gear.