A few comments
The C150 may be cheap to buy but it has a bit of a sting in the tail with corrosion issues around the main landing gear support that can cost a lot to fix, the C152 may cost a little more to buy but it is a very "sorted" aircraft with few AD's and most of the C150 "mistakes" corrected and an engine with a TBO of 2400 hours.
Flybymike The "traumahawk" as you call it was from a flying instruction point of view the best GA trainer to come out of the USA in the last thirty years, unfortunatly it now suffers from product support issues due to the 13000 hour spar life. This issue alone deters companys from producing parts for the aircraft and so makes it unatractive for a high use operation.
Gyrotyro I think you should take notice of Bllink182 today I spent 2 hours in the hangar fixing aircraft and 6 hours pushing paper for this EASA part M. Not only is part M costing the customer lots of money but it is also taking the experienced engineers away from supervising and checking the quality of the work to push paper, the result is going to be that some companys are going to suffer a reduction of oversight on the hangar floor.
Oversteer Aircraft engines run most of the time at 65-75% of max power output, a car engine spends most of it's working life producing 25% of rated power, Aircraft engines also spend a lot of time doing nothing, this lack of use is a killer when it comes to corrosion and finaly when your 200,000 mile car engine fails with a big bang you get out and walk, if an aircraft engine fails your survival is just a roll of the dice!