You pose an interesting set of questions.
If it were me, and I wanted a modern bike, I'd go find a different sport-touring frame, or complete bike, from the 80s (these kinds of bikes can be found regularly on ebay, in my experience. And for very cheap. Just wait for one similar in geometry to your Mondia), and set *that* bike up as your modern touring bike.
Or, find another Mondia to alter. They're around. Many were sold. A Juvela (Mondia under another name), just sold on ebay for very little money. That would have been a perfect candidate for modifications.
Or order a custom frame from one of the many frame-builders around. I'd suggest Bill Davidson, who has been known for making one of the best-riding touring frames you can get--and still does, far as I know--he's still making frames, and his prices are *very* reasonable for custom work.
A Rivendell might also be a good choice for this application, if you like their look.
Or, you could go exotic, and order a custom Alex Singer before the company ceases to build...
Your original Mondia I would restore back to its original condition, and I would not alter the rear-spacing. The Mondia Special was my first good bike (I had an orange one), and I found that if you were finicky with chain-length you could get a 14-28 freewheel to work with the 42/52 chainrings and the stock Nuovo Record derailleur. Not totally impractical, even for us old guys. The 28 cog will get you up most hills ok.
I'd also put the Campagnolo bar-ends back. Properly adjusted, these are still the nicest bar-ends around, better than the Suntours (and I never thought I'd say that: the key is getting them correctly adjusted, with appropriately thick, low-stretch cables. Touche, Stevan... ;> )
Were it me, I'd want the Mondia to be in its original condition, and I'd get a more modern sport-tourer for every-day use. Especially if the Mondia paint is still fairly clean. It was the great fade-paint scheme that makes the bikes what they are. To paint over the original paint and pinstripes would be unfortunate, in my view.
All this said, the Mondia is not a terribly collectible bike, so making major alterations to it is not going to spoil it especially (I do cringe at altering the rear-spacing, and at repainting it, but it's a purely irrational cringe), however, once you do it, of course, you can't go back. Better to have two bikes and alter one. Keep your old soldier in its original state.
My plugged nickle.
Charles Andrews SoCal
As for some new graphics for your Mondia, Jim Cunningham at CyclArt has them all, and he might be able to remove the tattered ones and replace them without doing much re-painting beyond a bit of touch-up and clear-coating. You might call him and check it out. Of course, doing much touching-up on a Mondia Special is going to run into some serious money, because of the pin-striping.