Do you have comps or a sweet spot to take advantage of a comp crawler? If not, I vote 4x4 slash also. I LOVE mine! Its easily top 2 of my favorite "fast/racer" rigs. Plus its WAY cheaper than a good comp rig and the price keeps dropping. I saw RPP has them the other day for $367 shipped!
You already have a killer scaler so you might as well get the slash! If we had comps in this area I would say build the crawler but i don't see that happening any time soon.
I do have great place to run a comp crawler but i have alot of great places to run a slash too.
Ok now its down to the rtr or the platinum. There isn't a huge difference in price and the platinum comes with some sweet stuff but i figure the rtr is probably durable as heck and i'm not competitively racing with it soooo. Plus i could sell the 2.4 radio and get back some more cash.......