The question of "to have or not to have" AC is up to each owner, but here are my thoughts/experiences:
When I was younger and living on the Calif beaches I never needed it. Now I'm old and live in Las Vegas and I could not survive without it.
So in my recent (non-Fiat) resto project I took the time to learn a lot about AC systems and how to add one to my classic Euro import. There are pros and cons of using the original 'factory style' vs. an aftermarket kit like Tony suggests. The old factory system has the benefit of fitting in the tight spaces well, but the technology has changed significantly since it was designed. Conversely, the new add-on kits have the improved technology (more on that in a moment), but will need to be fitted somehow. In the end I choose to make a hybrid of the two; using the factory mounts and drive pulleys for the compressor, and the factory evap box for under the dash...but fitted modern components for the rest (the compressor itself, condenser, receiver/dryer, expansion valve, evap core, and hoses).
Modern compressors, condensers, evap cores, receiver/dryers, expansion devices, etc are all WAY more efficient now compared to those of the '80s (or before). They will offer significantly more cooling with significantly less drag on the engine, and take up less space as well.
Here are a few considerations:
If you attempt to resurrect any 'used' system you will have problems unless you replace the compressor, condenser, receiver/dryer, expansion valve, and hoses with new parts, plus extensively flush the remaining components. The change to new refrigerant, oil, seal and hose materials, plus debris/contamination will destroy your system in short time if you don't. Therefore why not replace all of this with modern components rather than original type parts?
Doing so may require some modification/fabrication effort. The mounts may need slight alteration to fit the compressor, new hoses will need to be custom made (actually less expensive than buying new direct replacements), and you might have to design a couple tabs to fit the condenser and/or evap core.
But here is the kicker. Not only are the modern designed parts more efficient, they can actually be much less expensive. The condenser, receiver/dryer, compressor and possibly the evap core can be found as 'universal' fit items, or with a little research you can find suitable substitutes from readily available vehicles. All of which are really affordable. For example my recent project used a expansion valve that was difficult to find in a direct replacement. When I found one the price was around $130. With some online exploring I found the exact same valve was used on '90s Ford trucks and bought it for $9. (yes 9, not 90)! Even if your vehicle currently has NO AC components on it, I estimate you can build a complete system for around $500 (mine cost a total of $400, including finding the few 'factory' bits).
The really small cubic footage of the X1/9 interior makes it extremely easy to keep VERY cold if desired. And the highly efficient components available today will require very little drain on the engine.
In doing all of this research and learning about AC systems I got so excited that I also purchased the equipment needed to service them...new or old. It is actually very simple. So don't be afraid to tackle adding AC to your car. You can find pretty much everything you need on the internet [yeah, I even learned what THAT is].