I have an '05 S R53 w/ 160k miles. I have done the following
Rt & left front wheel knuckles
front inner & outer ball joints
front upper & lower control arms
Valve cover gasket & spark plug tube seals
ATI super damper harmonic pulley
15% Alta supercharger pulley, new serpentine belt
screaming demon coil pack
8.3 MM spark plug wires
colder heat range plugs
k&n air filter, stock box
new stock air hose to throttle body
drilled and slotted rotors brembo brakes
new power steering pump and all hoses/ resivior.

I love this little car and don't know if I continue to fix it up or part ways... I would do suspension, exhaust, headers... I know I'll need an engine and SC soon. Right? It runs great now but that's now and I drive the $#|t out of it.

I dove a 2013 fiat abarth and it was a blast. Totally different. Newer car obviously but love the exhaust notes.

Help me..torn r53 owner.

 

If the R53 is paid for then I'd fix what you have. Beats a car payment. Besides, the 500 is pretty tight on the inside. Also, the Fiat is still going through the learning phase where the bugs in the Mini are figured out.

That said, the Mini is 11 years old. Judgement call...

 

Or how about a low mileage 2013 R56s? I have one of those, have previously had an '03R53, and test drove a 500 Abarth several times. They are all fun and all have their pro's and con's. Personally, I prefer the R's over the 500: 6 speeds vs 5, better road feedback. The 500 felt overpowered to me, but maybe with some suspension mods that could be controlled. Definitely a nice exhaust note on the 500!

 

Everyone I have known who went from MINI to FIAT came back to MINI for many reasons. Including but not limited to wildly known crappy service....( usually for making customers pay for parts and labor for replacement of a poor quality part which mini would have clearly paid for.... )

Good luck if you do, you will need it.