So the guy asks how much something is worth. Who cares. Let's not get the Talk Bass Police involved. Jeesh. And if your CL or Ebay business is separate from here, then don't respond.
Anyway..
I saw a 2x15 in my local Guitar Center a few years ago, and the manager of my practice space recently bought one. The one I saw at GC was around $350, and it was in mint condition. I'm pissed I didn't pick it up. It sounded amazing. And I'm not a 15 kind of guy. I'd say see if you can bargain with the guy. If not, you've still got the 8x10. All I can say is from the 2 I've heard, they're pretty nice. But I do agree, it's overkill.
And if your 8x10 is getting muddy, maybe cut your lows a little bit. I've never had an 8x10 sound muddy, unless the lows are CRANKED.