Looking to modernize/upgrade my 20 years old tourer

It's good to do this sort of thing. About 10 years ago I did a bit of upgrading on my then 20ish y/o Trek 520 tourer. I got a disk fork for it because I wanted some decent stopping power for the loaded downhills. I used Avid cable disk brakes on the front and left the cantis on the back. Great bike made better! It convinced me that an all disk tourer was the way to go so I built up a titanium Lynskey disk Backroad tourer, and it's a nice loaded ride that I recently upgraded with Spyre cable disk brakes. The Trek languished for a while, but about 5 years ago I put a Bafang mid drive conversion kit onto it. Now it's got another new life as my go-to ebike when I'm a bit weary but still want to ride. The frame is the only thing remaining from the original 1994 purchase. All other bits have been upgraded or replaced as needed over the course of its 100,000kms life.

I also converted / upgraded my 36 year old steel tourer (Koga Miyata Radonneur) to a more modern gear set up and a wider gear ratio.  

The original setup was 2x6 speed Shimano Golden Arrow, the predessor of 105 with a freehub cassette with down tube shifters fro front and rear

However I also changed from drop handlebars to flat bars and that enable me to use a much wider range of components from moutain bike range.  

A) New rear wheel with Shimano cassette mount 11 speed

B) Rear Deraileur:   I used Shimano Deore 11 speed with long cage and a 11 to 36 cassette and a Deore flat bar shifter.  ( I already had tekto brakle levers which I used)    If you want to go a bit further you could also get Deore Brake levers and a direct mounted shifter for the cleanest set up.  

C) I kept the original front deraileur and the down tube shifter for it since I do not change the front chain ring often.  If you go for the deore brake levers you can then also get the shiting for the front deraileur on the handle bar and get rid of the remaining downtube shifter.  

 D) I got myself a "cable" end stop for the gear housing guide and located it near the location where the down tube shifter was for the rear deraileur. 

E) I changed to dual pivot rim brakes (Tektro R359 long drop) 

F) Final change was to go to smaller chain rings on the from from 52/36  to 50/34

I ride this bike on long 100 mile tours and it is a real pleasure   

I'm as guilty as anyone else of upgrading things for the sake of it, but if this lovely bike was mine, and everything is working OK at the moment, I would not do such a big upgrade. 9 speed parts are strong and relliable, there is nothing wrong with triple chainsets, brifters don't break very often, and upgrading to 105 won't save much (any?) weight.

Why not just rebuild the wheels with new rims and strong, single butted spokes? Probably replace the cassette and chain too. 

If you are worried about gear failures in remote places, you could buy a pair of down tube friction levers and stick them in your tool kit as an emergency backup - ~50g and the frame looks like it has braze ons for those already. Then you can use the €1500 you saved to extend your trip. I'm jealous!

Or, if determined to modernise, Shimano Tiagra is available with cable levers and would operate cantis. It is 10 speed not 11, but that is probably an advantage for touring. You could even keep the triple chainset as there is a Tiagra 3x shifter.