How long have you been looking for the Ariel Stitch without success, and how badly do you want it? That's more how I judge things. LE size, price...those are equitable. Even T/W is equitable. The "available pins per person wanting" is actually in the Ariel's favor. I don't know where things would be if Pinpics dropped the "inactive" traders/wants. Where the gap probably is, is Ebay prices. Tangled is $250, at a LE250, I doubt the Ariel Stitch is that high.
This is where I wouldn't necessarily need to squeeze every last drop of value out of the Tangled pin. If Ariel doesn't show up much, than is getting every last drop worth the trade off of possibly not being able to find another Ariel. Don't know what it cost your for the Tangled pin, and how that compares to the going rate for Ariel. Ah, I see one is up for $80 opening bid. So third option, buy pin, sell Tangled to cover pin costs, with money leftover to buy something else too.