JDJ,
I guess the money is just burning a hole in your pocket. Did you decide to just buy the plane for yourself or are you still thinking of instructing in it?
You've basically flown both airplanes. The C-150 is about as close to the C-152 as you can make two planes. The only major difference I can recall is the extra 10 degrees of flaps in the C-150. You can put the "barn doors" down to 40 degrees instead of just to 30 - a BIG difference when you are attempting a go-around with full flaps - just note that. Most of the airspeeds are 5 kts slower and I seem to remember that the C-150 is 1600 and the C-152 is 1670lbs gross.
As an older guy, I'm just tired of squeezing my frame into a C-150/152 cabin. It's like putting on a tight pair of gloves. Both are great little trainer planes. The others have a point that it is tempting to use all that room in the back of the Cherokee to put stuff or people, but if you follow the W&B for the airplane it handles as it should. The C-150 has no such temptation - you are always just figuring how much fuel you should put in the thing and hoping that your next student weighs less than you do.
As a Cherokee (180hp) owner, the only thing to watch out for these days are some of the AD's for older aircraft. Just got a scary one the other day about two aircraft (10,000 airframe hours and 12,000 airframe hours) that developed cracks in the Vertical Stab and the FAA's normal mumbo-jumbo about inspections in that area. That joins the Flap handle AD and the wing spar AD for things that are getting stressed on older aircraft.
Just make sure you get a good pre-buy inspection from an A&P who knows Piper or Cessna aircraft. Good luck. You would do well to search this forum for other buyer info - some good words have been passed to others who looked to buy.
The good thing about ownership is having a known entity out there on the ramp waiting for me to fly her. The problems are of course all money and time - insurance, tiedowns, maintenance, fuel & oil, taxes, maintenance, washing and waxing, maintenance, inspections, registrations and did I mention maintenance. You get the idea.