I have a pepper white 04 1/2 Cooper S.
She has the following list od accomplishments.
173k miles.
In the last 10k
New axel shafts.
All new suspenison.
All new brake lines.
JCW brake upgrade.
3 sets of tires and rims.
Winter steelies.
Stock alloys with run flats.
Lightweight alloys with summer ultra performance.
An installed serviced Supercharger.
an extra supercharger.
An extra intercooler.
Serviced Manual Trans with Royal Purple.
Black and Tan leather interior no rips.
New headliner.
New Spark plugs.
one ball mod.
All led headlights/signals with originals in boxes.
i would comfortably drive it to Antarctica.

Whats it worth?

Maybe $3k or so?

It would depend on when all that work was performed in relation to the current mileage (you've had 3 sets of tires in the last 10K miles?). What is a "one ball mod"? It would also depend on the amount of corrosion you have since you live in the salt belt, body, paint condition, and the condition of the interior. Detailed maintenance records help improve the car's value as well.

Check auto trader.com to see what similar MINIs selling prices.

"One ball mod" is a common exhaust mod that eliminates one of the two mufflers.