I can totally relate, as I was contemplating selling mine a month or so ago, when I was in the midst of trying to overcome the "Satanic Possession" issue I'd been having with the car ever since I'd owned it. The choice: spend the money to fix it, or sell it and run the high risk of buying another (worse) car with a whole new list of mysteries to solve and cosmetic issues to iron out.
Well, two months and $2,000 later (okay, so not all of that $2k was NEEDED) about the only thing I'm struggling with now is what color to repaint it in the spring. She runs like a champ and puts the smack down on the unfaithful (ricers). Had I sold it and bought something else, I'd still be spending all my days off with my head under the hood and/or my feet sticking out from under the side of the car, wrenching away at a whole new set of mechanical headaches. There is NO SUCH THING as a used car that doesn't need SOMETHING fixed - why else would they sell it?
In the long run, as I'm sure you'll find out, too, it's best to just stick with what you've got and make the best of it. Besides, with miles as low as you've got on there, you'd be shooting yourself in the foot to sell it; someone would see the miles, talk you way down on the price because of the body damage, and then after they snag it, they'll throw on a couple of parts, spray on a bit of color, and sell it for double what they bought it for (or drive the thing forever with a huge poopie-eating grin on their face

).
As far as the power steering, they cost less than $75 at most places (with a new reservoir), and take three hours or less to replace ... the hardest part being the process of removing and installing that stupid press-on pulley (you can buy the tool for less than $20 or rent it for free). Or, better still, just bypass the thing with a shorter belt and save your money for a Flaming River manual rack conversion and thus save weight and gain a couple of horses in the process.
Let's put numbers to it:
New rear GT bumper fascia: $160 (50resto.com)
Having a shop spray some black paint on it: $150? (Maaco will do the whole car for not much more than that)
New PAIR of rear LX tail lenses (may as well upgrade): $110 (50resto.com)
Reman Power Steering Pump w/reservoir AND pulley tool: $80 (Autozone)
GRAND TOTAL: $500. Whooptie-doo.
Seriously, guy. Save the 'Stang. Love it and it shall love you back.