BMW's are an entirely different driving experience.  If you want more of a
true sports car/small grand touring ride...then Porsche is for you.  If you
want more of a luxury, grand touring ride and experience, then most BMW's
are for you...except the Z's and a maybe the high powered "M" models
(similar to Mercedes AMG models).

That said, I have owned a number of Porsches since the '70's, and currently
own and drive an '01 cabriolet daily.

My car is just about to hit 40K miles, and I put about 8.5-9K mi per year,
so our maintenance should be about the same.

In basic terms, today's 996 cars operate on a daily basis much like any
other modern auto.  You turn the key and they run.   Put in fresh Mobil 1
and a filter every 5-7,500 miles and the engine might run forever.

One of the keys prior to purchasing any pre-owned Porsche is to have a
pre-purchase inspection by a knowledgeable shop...not the one that regularly
services the car you're having inspected, and try to get the service
records.

Known problem areas...or simply "wear" items:

1.  Brake pads should have been changed at least once
2.  The coolant "overflow" tank is "plastic"...and they have been known to
crack and drip down on the exhaust.
3.  Some of the early 3.4L engines (and some Boxster engines as well) had
leaky rear mail seals.  Those that are bad should have already come to light
and been changed...if required...on the car your're looking at.  Any
experienced Porsche technician should be checking for this on an inspection.
4.  In order to extract the last little bit of horsepower from the newer
cars, Porsche is using a lighter weight clutch disk...and these tend to wear
out much earlier than in the past.  See if the one on this car has been
changed, if not...it's going to need one soon.  Check the clutch
travel....if it engages in the last 2" or less...that's a sign that it's
getting time for replacement.  You can purchase the exact Sachs clutch that
Porsche uses from several direct importers for less than 1/2 what a dealer
will charge.  The labor...that's another thing.  At a dealer, it's over $1K,
but obviously less at independent shops.
5.  Make sure that your climate control instrument cluster is operating
properly, and that the LED's are reading out properly.  They are not a big
problem area, but if you need a replacement, it comes as a complete
assembly...and is not cheap.
6.  Same for the instrument cluster...tach, speedo, gas, oil pressure, temp,
etc.
7.  The factory installed radios are not well thought of...and are not the
best in the world...by a long shot.  The good news is that excellent
replacements are available from any experienced car stereo shop.  Be careful
who you let do any work...try to use someone who is experienced with
Porsches, BMW's, etc.
8.  Try to get all the keys for the car...which should include 2 master keys
w/remote door/trunk opening, and one valet key.  Getting new keys is not
easy and not cheap.

The new cars have good climate control (A/C-Heat) and are generally much
better daily drivers than the older cars.  Maintenance is not a major
problem these days; however, make sure that you get a comprehensive
mechanical/electronic inspection and review all service records.  If all is
OK and the exterior and interior are in good shape...to meet your standards,
enjoy.

Hope this helps.