I've got a 2006 Mini Cooper S with about 55,000 miles on it and i'm looking to upgrade the old girl. I believe i'm at 168HP now...
What can i practically expect as far as performance boosts? Let's say my budget is an absolute max of $1,000.
Can i expect to see something like a 5 horsepower boost or a 50 horsepower boost? (Would i be able to notice a 5HP boost?)

I guess what i'm asking is, what upgrades offer the most bang for the buck?
I've heard exhaust, air intake and computer management are good ones...
Also, i know almost nothing about all of this, but dont mind learning...

Thanks for the help.

Best bang for the buck is fitting a 15% reduction supercharger pulley plus colder spark plugs.

About 20 more horsepower for the cost of 3 hours labor plus the cost of the pulley, smaller belt and plugs.

Airfilter, exhaust. (about 10hp on a UK car)
Only do the pulley with a bigger intercooler or you "may" cook your engine.
and uprate your brakes, they are only just good enough for a standard car.

If you consider handling a part of performance, then definately a rear sway bar. I installed a 22mm rear sway bar recently and regret that I didn't do that 5 years ago. It's another great bang for the buck performance mod.

Only do the pulley with a bigger intercooler or you "may" cook your engine.

A larger intercooler is not required for a 15% reduction pulley.