changing spark plugs sucks, but I wouldnt farm it out for $300... Unblot the motor mount, and pry on the block... OR, just put some $$ ones in there on the new engine, and run them for 5 years. The engine it allready out of the car, spend another $100 on exelent quallity spark plugs, and wires.
I like GM products, cause they're CHEAP. It's extreamly easy to get parts for that car, if u need ANYTHING, I can go junkyarding for you...
how's the transmission? IF it's had good fluid maintiance, I'd keep the car.
It's a decent car, mabey you should do an L67 swap
... 3.8...
I'd keep it, and have it fixed... If you dont think you'll get much for resale, think of the depreciation on a NEW car...
I'd be half tempted to buy a GOOD $4k car, and be prepaired to spend another grand tops on it making it perfect...
Good luck
~Nate