Thank you for all of your feedback. I'm getting the impression that this might not be the right plane for me (at the current price anyway). I'm concerned that the low-time and leather seats are the 2 big things that keep catching my eye. If the base price of a 1977 150 M really is $21,400 like Vref says, it does seem pretty silly to pay $14,000 for upgrades in a plane that doesn't have a perfect panel.
I have around $35,000 to spend on my first aircraft. I would prefer a "perfect" 150 or 152 to a "less than perfect" 172. I would rather buy a plane that is already close to perfect (I think) than buy a plane that is average and spend a ton of time and money upgrading it myself.