I keep my LT1 because I have already invested in it. Besides, I like to be a little different. Seems like every swinging dick these days has an LS1. And for good reason, it's a better power plant than an LT1, but nobody ever accused me of being smart.
$5500 sounds like a decent offer depending on what you mods are, but regardless I doubt you'll get more. So, just to muddy the waters a bit I'll toss out another option. If the chassis is in good condition, keep the car, build an LS1 to swap in. Continue to drive and enjoy the car while building the power train you want. When the time is right do the swap.
You're better off with an LS motor, but I'll keep tilting at windmills.